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HISTOLOGY 

RADASCH 


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FQUIZ-COMPENDS? 


A  COMPEND 


OF 


HISTOLOGY 


HENRY  ERDMANNJRADASCH,  M.S.,  M.D. 

ASSOCIATE   IN    HISTOLOGY  AND  EMBRYOLOGY   IN   THE  JEFFERSON    MEDICAL 
college;    FORMERLY    FELLOW    IN    CHEMISTRY    IN    THE    UNIVER- 
SITY    OF     IOWA      (1895-6)  ;     FORMERLY     LECTURER     ON 
CHEMISTRY    AND    DIRECTOR    OF    THE    CHEMICAL 
LABORATORIES     IN     THE     COLLEGE     OF 
PHYSICIANS       AND       SURGEONS 
KEOKUK^    IOWA    (1897-8). 


Wxtii  Ntnrtg-nglit  SfUuBtrattona 


qtv\55\ 


Philadelphia  : 

P.  BLAKISTON'S  SON  &  CO. 

1012  Walnut  Street. 

1905. 


A7  4\A 


Copyright,  1905,  by  P.  Blakiston's  Son  &  Co. 


PRESS    OF 

REPORT    PUBLISHING    CO. 

Lebanon,   Pa. 


TO 


THIS   VOLUME    IS   AFFECTIONATELY    DEDICATED 


524  \^ 


P.R£FA:e^E 


It  has  been  the  author's  purpose  to  supply  a  volume  more 
complete  than  the  existing  compends,  and  yet  not  so  volum- 
inous as  a  Text-book.  An  effort  has  been  made  to  present 
the  matter  in  a  clear  and  concise  manner,  and  as  up-to-date 
as  possible. 

The  subject  of  Embryology  has  been  touched  upon  only 
in  so  far  as  it  bears  directly  upon  the  Histology. 

The  chapter  on  Technic  has  been  made  as  complete  as  is 
necessary  for  routine  histologic  and  pathologic  work.  The 
Connective  Tissues  have  been  grouped  in  what  seems  a 
simple  and  also  characteristic  manner.  The  Blood  Cells 
have  also  been  arranged  in  a  simple  and  readily-compre- 
hended form. 

The  chapter  on  Placenta  and  Umbilical  Cord  has,  how- 
ever, been  written  somewhat  in  detail,  as  the  embryology  of 
these  organs  is  essential  for  a  thorough  knowledge  of  their 
structure.  The  illustrations  are  from  the  works  of  Prof. 
Minot,  to  whom  the  writer  is  indebted  for  their  use. 

The  forty-seven  new  cuts  were  prepared  under  the  direc- 
tion of  Dr.  H.  H.  Cushing.  Of  these,  twenty-seven  are 
from  slides,  while  the  remainder  represent  modifications  of 
current  Text-book  figures. 

The  writer  desires  to  thank  Dr.  R.  C.  Rosenberger  for 
his  assistance  in  proof-reading  and  suggestions,  and  the 
publishers  for  their  many  kindnesses  and  courtesies. 

914  South  Forty-seventh  Street,  Philadelphia. 
August,  1905. 


vu. 


CONTENTS. 


'  PAGE. 

CHAPTER   I. 
Technic    i 

CHAPTER  n. 
The   Cell 28 

CHAPTER   HI. 
The  Tissues — Epithelial  Tissues 41 

CHAPTER   IV. 
Connective    Tissues 53 

CHAPTER   V. 
Muscular   Tissues 72 

CHAPTER  VI. 
Nervous    Tissues 78 

CHAPTER  VII. 
Circulatory    System 88 

CHAPTER  VIII. 
Lymphatic    System ICXD 

CHAPTER   IX. 
Alimentary    Tract 106 

CHAPTER  X. 
Digestive    Glands 132 

CHAPTER  XI. 

Respiratory  System  and  Thyroid  Body 142 

ix. 


X.  CONTENTS. 

PAGE. 

CHAPTER  XII. 
Urinary  System  and  Adrenal 154 

•      CHAPTER  XIII. 
Male  Genital   System 169 

CHAPTER  XIV. 
Female  Genital   System 182 

CHAPTER  XV. 
Placenta  and  Umbilical  Cord 198 

CHAPTER  XVI. 
Skin  and  Its  Appendages 211 

CHAPTER  XVII. 
Nervous    System 226 

CHAPTER  XVIII. 
Eyeball  and  Lacrimal  Apparatus 245 

CHAPTER  XIX. 
The    Ear 2(i^ 

CHAPTER  XX. 
The  Senses  of  Smell,  Taste  and  Touch 280 


LIST  OF   ILLUSTRATIONS 


FIG.  PAGE. 

1.  The    Cell    29 

2.  Karyokinesis,   Close    Coil    32 

3.  Karyokinesis,  Loose  Coil   33 

4.  Karyokinesis,    Equatorial    Plate    34 

5.  Karyokinesis,    Nuclear    Spindle    35 

6.  Karyokinesis,    Daughter   Stars    36 

7.  Karyokinesis,  Daughter  Cells    ^6 

8.  The    Ovum    38 

9.  Simple  Squamous  and  Cuboidal  Epithelial  Cells 42 

10.  Squamous  Cell  of  Frog's  Skin   (surface  view) 42 

11.  Squamous    Cell,    Isolated    42 

12.  Stratified    Squamous   Epithelium    42 

13.  Simple  Columnar,  Ciliated  and  Goblet  Cells 43 

14.  Isolated    Columnar    and    Ciliated    Cells ;    Goblet    Cells    in 

Various    Stages     43 

15.  Pseudostratified    Cells    44 

16.  Stratified  Columnar,  Ciliated  and  Goblet  Cells 45 

17.  Transitional    Cells    45 

18.  Various   Forms  of  Endothelial  Cells 47 

19.  Simple  Tubular  Gland  from  Large  Intestine 49 

20.  Diagram   of   Tubular    Glands 51 

21.  Diagram  of  Alveolo-tubular  Glands 51 

22.  Diagram   of   Alveolar  Glands 52 

23.  Varieties   of   Connective  Tissue. '  54 

24.  White  Fibrous  Tissue 56 

25.  Varieties  of  Cartilage    6z 

26.  Cross-section    of    Compact    Bone 65 

27.  Cross-section  of  Developing  Bone 70 

28.  Varieties    of   Muscular   Tissue 74 

29.  Nerve   Cells   and   Fibres 81 

30.  Tactile    Cells    83 

31.  Corpuscle  of   Meissner    84 

32.  Pacinian   Body    85 

^2,-  Motor    Nerve-endings    86 

34.  Tendon-spindle 87 

xi. 


Xll.  LIST  OF  ILLUSTRATIONS. 

FIG.  PAGE. 

35.     Cross-section  of  a  Medium-sized  Artery.... 91 

^6.     Cross-section  of  a  Vein 93 

Z7.    Forms   of   Blood    Cells 95 

38.  White  Blood  Cells   96 

39.  Hemin    Crystals    98 

40.  Hemoglobin    Crystals     98 

41.  Section  of  a  Human  Lymph  Node loi 

42.  Section  of  the  Spleen    103 

43.  Section  of  the  Thymus  Body   105 

44.  Longitudinal   Section  of  a  Tooth 108 

45.  Cross-section   of   the  Tongue 112 

46.  Vertical  Section  of  a  Human  Tonsil 114 

47.  Cross-section  of  a  Human  Esophagus 116 

48.  Section  of  the  Cardiac  End  of  the  Stomach 119 

49.  Section  of  the  Pyloric  End  of  the  Stomach 121 

50.  Section  of  the  Duodenum 123 

51.  Longitudinal   Section  of  a  Villus 124 

52.  Cross-section  of  the   Ileum 125 

SZ'     Cross-section  of  the  Colon 127 

54.  Cross-section   of   the   Human   Appendix 129 

55.  Section   of   Pig's   Liver 133 

56.  Section   of   Human    Pancreas 140 

57.  Section  of  the  Submaxillary  Gland  of  a  Fox 141 

58.  Cross-section  of  Trachea 145 

59.  Section  of  Human  Lung 147 

60.  Section  of  Human  Thyroid  Body 152 

61.  Section   of   Human   Kidney 155 

62.  Section   of   Injected    Kidney 159 

6^.     Sections  of  Human  Ureter  and  Bladder 162 

64.  Section   of   Human    Adrenal 167 

65.  Section    of   Human    Testicle -. 170 

66.  Human    Spermatozoa    176 

67.  Section  of  a  Human   Prostate 178 

68.  Cross-section  of  an  Ovary  of  a  Cat 183 

69.  Ovum  of  a  Cow 185 

70.  Cross-section  of  a  Human  Fallopian  Tube 189 

71.  Resting  Uterine   Mucosa    191 

72.  Cross-section  of  a  Human  Vagina 194 

7^.    Diagram  of  Development  of  Primates 199 


LIST  OF  ILLUSTRATIONS.  XUl. 

FIG.  PAGE. 

74.  Diagram  of  Development  of  Primates 200 

75.  Diagram  of  Development  of   Primates 202 

yd.  Semi-diagrammatic  Outline  of  Uterus  and  Embryo 204 

TJ.  Human    Placenta    at    Term 206 

.  78.  Cross-section  of  the  Human  Umbilical  Cord 208 

79.  Cross-section  of  the  Skin  of  the  Sole  of  the  Foot .....  213 

80.  Section    of    Scalp   Hair 216 

81.  Cross-section  of  a   Nail 219 

82.  Section  of  a  Lactating  Human  Mammary  Gland 222 

83.  Vertical  Section  of  Human  Cerebral  Cortex 228 

84.  Vertical   Section  of  Human   Cerebellar   Cortex 233 

85.  Cross-section  of  Human  Spinal  Cord 239 

86.  Corneo-Scleral   Junction   of    Man 248 

87.  Vertical  Section  of  the  Retina  of  a  Rabbit 252 

88.  Cells  from  the  Retina  of  an  Ape 255 

89.  Vessels    of   the   Eye 260 

90.  Section   of  the  Eyelid 263 

91.  Horizontal  Section  of  the  Internal  Ear  of  a  Kitten 273 

92.  Scheme  of  the  Structure  of  the  Tympanic  Wall 274 

93.  Corti's    Organ    276 

94.  Diagram    of   Olfactory    Mucosa 280 

95.  Isolated   Cells   of  Olfactory   Mucosa 281 

96.  Taste-Bud  from  the  Papilla  Foliata  of  a  Rabbit 282 

97.  Corpuscle  of  Wagner    283 

98.  Pacinian    Body    284 


CHAPTER  I. 


TECHNIC. 

For  a  thorough  understanding  of  Histology  a  knowledge 
of  Technic  is  requisite,  as  sections  for  study  must  be 
properly  prepared,  and  this  requires  skill  and  care. 

The  various  steps  necessary  to  prepare  a  piece  of  tissue  for 
sectioning  are  Fixation,  Dehydration,  Clearing  and  In- 
filtration. 

FIXATION. 
Fixation  is  the  process  by  which  the  intercellular  sub- 
stance and  the  protoplasm  of  the  cells  are  coagulated  by  the 
aid  of  solutions  thereby  keeping  them  as  nearly  like  normal 
as  possible.  Such  solutions  are  fixing  fluids,  of  which 
there  are  a  great  many  combinations.  Simple  fixatives  which 
are  not  numerous,  will  be  given  first,  and  under  each,  its 
combinations. 

1.  Heidenhain's  Solution  consists  of  a  saturated  solu- 
tion of  bichlorid  of  mercury  in  a  normal  salt  solution. 

Bichlorid   of   mercury 112  gms. 

Sodium   chlorid 5  gms. 

Water 1000  c.c. 

Add  the  bichlorid  to  the  hot  salt  solution  and  when  dis- 
solved set  aside  to  cool.  The  excess  of  bichlorid  will  crys- 
tallize and  keep  the  solution  saturated. 

Three  to  five  per  cent,  of  glacial  acetic  acid  aids  the  pene- 
tration of  the  bichlorid  and  assures  more  thorough  fixation. 

This  solution  requires  from  two  to  four  hours  to  fix  one- 
half-inch  cubes. 

2.  Potassium  Bichromate. — This  salt  in  a  solution  of 
three  and  one-half  per  cent,  strength  is  a  good  fixative  and 


2  TECH  NIC. 

hardener.  The  strength  is  gradually  increased  one-half  of 
one  per  cent,  by  frequent  renewal,  to  sir  per  cent.,  in  the 
course  of  six  weeks.  It  will  not  injure  tissues  left  in  it  for 
a  longer  time.  It  is  not  often  used  alone  but  in  combina- 
tions mentioned  below. 

a.  Zenker's  Fluid  is  a  mixture  of  Miiller's  fluid  and 
bichlorid  of  mercury. 

Miiller's   fluid looo  c.c. 

Corrosive  sublimate 112  gms. 

Mix  and  add  before  use 

Glacial  acetic  acid 50  c.c. 

This  solution  requires  from  twelve  to  twenty-four  hours 
to  act  and  should  be  freshly  prepared  each  time  before  using. 

b.  Tellyesnicky's  Fluid  consists  of  a  three  per  cent,  so- 
lution of  potassium  bichromate  to  which  is  added  five  per 
cent,  of  glacial  acetic  acid  (5  c.  c.  per  100).  It  is  allowed  to 
act  twelve  to  twenty-four  hours  and  then  the  tissues  are 
thoroughly  washed  and  dehydrated.  Nuclei  are  better  pre- 
served by  this  solution  than  by  the  usual  bichromate  mix- 
tures. 

c.  Miiller's  Fluid  depends  upon  potassium  bichromate 
for  its  action.    Penetration  is  aided  by  sodium  sulphate. 

Potassium  bichromate 60  gms. 

Sodium   sulphate 30  gms. 

Water 3000  c.c. 

This  solution  requires  from  three  to  six  weeks  for  fixing, 
but  a  longer  time  does  not  injure  the  tissues.  It  is  commonly 
used  in  the  dark,  and  renewed  as  often  as  it  becomes  cloudy. 

d.  Kopsch's  Fluid  is  a  combination  of  potassium  bichro- 
mate and  formalin. 

Potassium  bichromate    (3.5%)    .      .      .      .      .80  parts. 
Formalin    (40%) 20  parts. 


FIXING    SOLUTIONS.  3 

The  tissue  remains  in  this  sohition  for  about  twenty-four 
hours,  and  is  then  transferred  to  a  3.5  per  cent,  solution  of 
potassium  bichromate  for  three  or  four  days.  It  should  then 
be  thoroughly  washed  and  dehydrated.  This  solution  is 
especially  adapted  to  the  nervous  system. 

Other  combinations  of  this  class  are  Orth's,  Erlicki's  and 
Bensley's  solutions. 

3.  Chromic  Acid  is  generally  used  in  .1  to  .5  per  cent, 
solutions,  and  should  be  allowed  to  act  one  to  eight  days,  as 
it  penetrates  slowly.  It  is  especially  adapted  to  connective 
tissues  and  where  mitotic  figures  are  to  be  studied. 

4.  Osmic  Acid. — This  reagent  is  used  in  .1  to  i  per  cent, 
solutions  as  well  as  in  combination  with  others.  It  is  a  spe- 
cific reagent  for  adipose  tissue  but  if  turpentine  or  alcohol- 
ether  is  used  for  clearing  the  osmicated  fat  will  be  removed. 
The  time  for  fixation  depends  upon  the  strength,  usually 
from  twelve  to  twenty-four  hours  for  i  per  cent,  solutions. 

a.  Flemming's  Solution: 

Osmic  acid   (2%  solution) 2  c.c. 

Chromic  acid   (1%  solution) 45  c.c. 

Glacial   acetic   acid 3  c.c. 

This  solution  which  fixes  the  tissues  in  from  one  to  two 
days,  although  a  longer  time  will  not  injure  them,  should  be 
changed  at  least  once.  The  tissues  are  then  thoroughly 
washed  and  dehydrated.  This  fluid,  which  is  good  for  the 
study  of  mitotic  figures,  should  be  prepared  just  before  using, 
as  it  does  not  keep. 

b.  Golgi's  Solution: 

Osmic  acid   (2%  solution) 3  c.c. 

Potassium  bichromate   (3.5%  solution)    ...     25  c.c. 

Fix  three,  five  or  seven  days  and  transfer  to  silver  nitrate. 
This  is  used  especially  in  the  Nervous  System.  The  details 
of  the  process  will  be  described  under  Silver  Staining. 


4  TECHNIC. 

5.  Formalin  is  a  saturated  solution  of  Formaldehyde 
Gas  in  water.  It  is  not  used  in  full  strength,  but  usually  as 
a  4  to  10  per  cent,  solution.  A  4  per  cent,  solution  is  pre- 
pared as  follows : 

Formalin 10  c.c. 

Sodium  chlorid  (.5%  solution) 90  c.c. 

This  requires  from  twelve  to  twenty-four  hours  for  its 
action,  and  is  especially  useful  in  the  nervous  system.  It 
may  be  used  with  potassium  bichromate  as  above  given. 

6.  Nitric  Acid  is  used  as  a  j  per  cent,  soliiiion,  and  small 
pieces  of  tissue  are  allowed  to  remain  therein  from  one-half 
to  one  hour.  Large  specimens  (embryos)  require  from  four 
to  eight  hours.  After  fixation  the  tissues  are  immediately 
transferred  to  70  per  cent,  alcohol. 

It  is  especially  adapted  to  connective  tissues,  ova  and 
embryos. 

7.  Alcohol. — There  are  several  strengths  of  alcohol  suit- 
able for  fixation.  Besides  acting  as  fixatives  they  at  the 
same  time  dehydrate. 

a.  Absolute  Alcohol. — This  should  be  of  at  least  99.2 
per  cent,  strength.  It  acts  very  rapidly  and  thoroughly  but 
its  expense  prevents  its  routine  use.  It  must  be  changed 
several  times.  After  twenty-four  to  forty-eight  hours  the 
tissues  are  ready  to  be  cleared. 

b.  Ninety-five  Per  Cent.  Alcohol  acts  in  the  same  way 
as  the  above,  but  some  (Mallory  and  Wright)  hold  that 
shrinkage  results  if  any  solution  weaker  than  the  absolute 
alcohol  is  used.  This  strength  has  however  yielded  good 
results  in  the  nervous  system.  It  must  be  frequently  renewed 

Tissues  that  have  been  fixed  in  solutions  containing  either 
osmic  acid  or  chromium  salts  must  he  thoroughly  washed  be- 
fore dehydration.  Golgi's  method  of  staining  is  an  excep- 
tion as  will  be  seen  when  its  steps  are  considered. 


DEHYDRATION.  5 

Blood  spreads  are  readily  fixed  in  a  solution  of  equal 
parts  of  absolute  alcohol  and  ether,  in  which  they  are  al- 
lowed to  remain  from  twenty  minutes  to  an  hour.  Another 
good  fixative  is  absolute  alcohol,  nine  parts,  and  formalin, 
one  part.    The  time  for  fixing  is  about  the  same. 

The  blood  spreads  may  be  subjected  to  a  temperature  of 
120°  C.  for  twenty  m'inutes.  Ehrlich  prefers  this  method  of 
fixation  to  the  above. 

DEHYDRATION. 

After  the  tissues  have  been  fixed  in  one  of  the  above  solu- 
tions and  washed,  they  are  ready  for  the  second  step,  that  of 
Dehydration. 

Dehydration,  or  Hardening,  is  the  removal  of  the  water 
from  the  tissues,  and  is  accomplished  by  alcohols  of  ascend- 
ing strengths.  The  tissues  are  transferred  to  a  fifty  per 
CENT,  solution  for  six  to  twenty-four  hours,  unless  other- 
wise directed.  This  is  followed  by  immersion  in  a  seventy 
PER  CENT,  solution  for  the  same  time,  and  then  in  a  ninety- 
five  PER  CENT,  solution  for  at  least  twenty-four  hours.  Dur- 
ing this  time,  the  last  should  be  changed  once.  To  in- 
sure perfect  dehydration,  the  specimens,  after  being  drained, 
may  be  placed  in  absolute  alcohol  for  twelve  to  twenty-four 
hours. 

If  the  following  steps  are  not  to  be  carried  out  immediately 
the  tissues  shall  be  transferred  to  a  solution  of  seventy  or 
eighty  per  cent,  alcohol  in  which  they  may  remain  in- 
definitely. 

CLEARING. 

After  dehydration  is  completed  the  tissues  are  ready  for 
the  clearing  agents. 

Clearing  is  the  process  by  which  the  alcohol  is  removed 
and  an  agent  that  will  mix  with  the  infiltration  medium  sub- 


6  TECHNIC. 

stituted.  If  paraffin  is  to  be  used  an  oil,  or  fluid  miscible 
with  both  alcohol  and  paraffin  is  necessary ;  if  celloidin  in- 
filtration is  to  follow,  then  a  mixture  of  alcohol  and  ether 
is  used. 

For  the  paraffin  method  the  tissues  are  removed  from  the 
alcohol,  drained  a  few  minutes  and  then  transferred  usually 
to  an  oil,  for  twenty-four  hours.  The  oil  penetrates  the 
tissues,  removes  the  alcohol  and  remains  in  its  place. 

Chloroform,  xylol,  and  various  oils  may  be  employed, 
among  them  being  turpentine,  which  usually  requires 
twenty-four  hours  for  half-inch  cubes. 

Xylol  requires  from  six  to  twenty-four  hours,  or  until 
the  tissue  is  transparent. 

Cedar  oil  is  used  as  follows :  The  tissues  are  first  placed 
in  a  mixture  of  equal  parts  of  cedar  oil  and  absolute  alcohol 
for  twenty-four  hours.  They  are  then  drained  and  placed  in 
pure  cedar  oil  for  the  same  length  of  time.  If  pure  oil  alone 
is  used,  it  is  changed  several  times  until  the  tissues  are  trans- 
parent, which  usually  requires  twenty-four  to  forty-eight 
hours. 

INFILTRATION. 

After  clearing,  the  tissues  are  ready  for  Infiltration. 

Infiltration  is  the  process  by  which  the  interstices  of  the 
tissue  are  filled  with  an  agent  that  hardens  and  allows  the 
tissue  to  be  cut  without  distortion.  There  are  two  impor- 
tant agents.  Paraffin  and  Celloidin.  Gum  may  be  used 
for  special  purposes.  The  paraffin  method  will  first  be  con- 
sidered. 

After  clearing,  the  tissues  are  drained,  blotted  with  tissue 
paper,  and  then  placed  in  a  tube  of  melted  paraffin,  at  a  tem- 
perature a  little  above  the  melting  point,  usually  50°  to  55°  C. 
This  is  called  Paraffin  No.  i,  and  its  object  is  the  removal 
of  the  bulk  of  the  oil.     After  twenty-four  hours  the  tissues 


INFILTRATION.  7 

are  removed  to  a  tube  of  fresh  paraffin  and  allowed  to  re- 
main the  same  length  of  time.  This  is  Paraffin  No.  2,  and 
the  remainder  of  the  oil  is  removed  and  pure  paraffin  left  in 
the  tissues.    The  tissues  are  then  ready  to  be  blocked. 

By  the  use  of  chloroform,  infiltration  with  paraffin  can 
be  accomplished,  to  great  extent,  in  the  cold.  The  tissues  are 
completely  dehydrated  with  absolute  alcohol  and  then  placed 
in  PURE  CHLOROFORM  to  replace  the  alcohol.  This  is  ac- 
complished when  the  tissues  become  submerged,  usually  four 
to  eight  hours.  They  are  then  transferred  to  a  warm,  satur- 
ated solution  of  paraffin  in  chloroform,  for  two  to  four  hours, 
and  then  to  pure  melted  paraffin  until  all  the  chloroform  has 
disappeared  (two  to  twelve  hours). 

If  delicate  structures  are  to  be  infiltrated  they  may  be 
cleared  slowly  by  adding  toluol,  or  benzol,  drop  by  drop 
to  the  specimen  in  absolute  alcohol  and  mixing  after  each  ad- 
dition. By  this  method,  2  c.c.  of  oil  can  be  added  to  the  same 
amount  of  absolute  alcohol  in  four  to  six  hours  and  no 
shrinkage  result.  The  specimens  may  then  be  transferred  to 
a  mixture  of  absolute  alcohol  (i  part)  and  toluol  (3  parts) 
for  one  to  three  hours.  They  may  then  be  placed  in  pure 
toluol  from  one  to  four  hours,  the  time  depending  upon  the 
size,  one-eighth  to  one-fourth  inch  in  diameter.  From  this 
it  may  be  transferred  to  a  solution  of  paraffin  in  toluol  for 
two  to  four  hours,  after  which  more  paraffin  is  added,  and 
the  tube  transferred  to  the  paraffin-bath,  where  it  remains 
for  an  hour  or  two,  and  is  then  cast. 

Blocking  may  be  accomplished  by  the  use  of  leaden 
angles,  paper  boxes,  or  zi/ooden  blocks.  The  leaden  angles 
are  of  various  sizes  and  are  used  in  connection  with  brass 
plates.  These  are  all  cooled  in  ice  water,  quickly  dried  and 
the  angles  put  into  place.  A  small  layer  of  paraffin  is  then 
run  into  the  mold,  and  the  tissue  placed  therein,  and  oriented. 


8  TECHNIC. 

The  mold  is  then  filled  with  melted  paraffin,  and  as  scK)n  as  a 
scum  is  formed,  the  whole  is  immersed  in  ice-water,  and  the 
angles  cautiously  removed,  so  that  the  water  can  act  upon  all 
sides  except  the  bottom.  Unless  this  is  done,  the  paraffin,  in 
cooling  rapidly  and  contracting,  will  enclose  water  bubbles 
that  are  unnecessary  and  annoying.  A  little  skill  is  required 
to  cast  successfully.  Usually,  by  this  method,  the  paraffin 
remains  clear,  a  condition  much  to  be  desired.  A  cup  is  pre- 
pared upon  the  end  of  a  block,  by  wrapping  a  strip  of  news- 
paper, five  inches  long  and  two  inches  wide,  tightly  around 
one  end  of  the  block,  and  sealing  with  paraffin. 

If  BLOCKS  are  used,  these  should  be  preferably  of  oak,  an 
inch  and  a  quarter  long,  by  seven-eighths  square.  The  end  is 
carefully  and  tightly  wrapped  with  a  strip  of  thin  paper, 
forming  a  cup  one-half  to  one  inch  deep.  The  specimen  is 
then  quickly  oriented  upon  a  thin  layer  of  paraffin,  and  the 
cup  filled  with  paraffin.  It  is  then  set  aside  and  allowed  to 
cool.  The  enclosed  air-bubbles  rise.  The  paraffin  is  usually 
not  clear  by  this  method,  but  is  made  so  by  placing  the  block, 
for  several  days,  upon  the  paraffin  bath.  The  warmth  clears 
the  paraffin. 

After  casting,  the  blocks  are  trimmed,  and  are  then  ready 
to  be  cut  with  the  microtome. 

For  the  celloidin  infiltration  method,  fixation  and 
DEHYDRATION  are  carried  out  in  the  same  manner  as  for  par- 
affin, but  a  different  clearing  agent  is  used.  A  mixture  of 
equal  parts  of  absolute  alcohol  and  ether  will  clear  tissues  in 
twenty-four  hours,  at  the  end  of  which  time  they  are 
ready  for  the  celloidin. 

Celloidin,  or  pyroxylin  is  used  in  two  different  solutions 
— thick  and  thin.  The  thick  solu-tion  is  prepared  by  dissolv- 
ing one  ounce  of  the  celloidin  in  a  mixture  of  150  c.c.  each  of 
absolute  alcohol  and  ether.    It  is  best  to  soften  the  celloidin 


INFILTRATION.  9 

for  some  hours  in  the  absolute  alcohol,  and  then  add  the 
ether.  Preserve  in  a  magnesium  citrate  bottle.  The  thin 
celloidin  is  made  by  diluting  the  thick  with  an  equal  part  of 
the  alcohol  and  ether  mixture. 

After  clearing,  the  tissues  are  drained  for  a  few  seconds, 
and  then  transferred  to  the  thin  celloidin  for  one  to  four  days, 
and  then  to  the  thick  for  four  to  seven  days.  They  are  then 
ready  to  be  cast. 

The  tissues  may  be  blocked,  as  in  the  paraffin  method,  by 
placing  the  specimen  in  a  paper  cup,  as  above,  upon  a  wooden, 
vulcanite,  composition,  or  glass  block,  and  covering  with 
thick  celloidin.  They  are  then  set  aside  until  a  thin  scum 
forms,  due  to  the  contact  with  the  air,  after  which  they  are 
placed  in  eighty  per  cent  alcohol  to  harden  the  celloidin.  In 
twenty-four  to  forty-eight  hours,  they  are  ready  to  cut. 

Another  way  to  cast  is  to  place  the  tissues  in  low  Stender 
dishes,  cover  well  with  very  thick  celloidin,  and  orient  imme- 
diately. When  a  scum  has  formed,  the  dishes  are  lowered 
into  another  containing  the  alcohol  for  hardening. 

Still  another  way  is  to  place  the  tissues  with  thick  celloidin 
in  stoppered  paraffin  tubes,  and,  after  several  days,  loosen 
the  stopper  and  allow  the  alcohol  and  ether  to  gradually  es- 
cape. When  the  celloidin  has  retracted  from  the  sides,  the 
mold  is  lifted  out  and  placed  in  the  alcohol. 

If  the  celloidin  is  not  hard  enough,  the  blocks  may  be 
placed,  for  twenty-four  to  forty-eight  hours,  in  eighty  per 
cent,  alcohol,  containing  i  to  5  per  cent,  glycerin. 


Gum.     This  infiltration  medium  is  prepared  as  follows : 

Cane   Sugar 28.5  gms 

Water 30     c.c. 


Syrup  i 


Cane   Sugar 28.5  gms. 

Water 30     c.c. 

(  Gum   Acacia 57     gms. 


Gum  <  .^.  ^ 

1  Water 310     c.c, 


lO  TECIINIC. 

Mix  together  four  parts  of  the  syrup,  five  parts  of  the  gum 
and  to  this  add  nine  parts  of  a  saturated  solution  of  boric 
acid.     Filter  through  muslin. 

The  tissues  are  thoroughly  washed,  free  of  any  trace  of 
alcohol,  and  are  then  placed  in  the  above  solution,  and  al- 
lowed to  remain  until  penetrated,  which  requires  at  least 
twenty-four  hours,  if  half-inch  cubes  are  used.  A  longer 
time  is  better.  The  process  is  aided  by  allowing  the  jar  with 
the  tissues  to  stand  in  a  warm  place. 

Tissues  infiltrated  with  gum  must  be  frozen  and  cut  in  a 
freezing  microtome. 

After  the  above  steps  have  been  finished,  the  tissues  are 
ready  to  be  sectioned. 

Paraffin  blocks  are  aU  dry,  the  knife  of  the  microtome 
being  placed  so  that  it  meets  the  block  squarely.  When  large 
objects  are  cut,  it  is  sometimes  necessary  to  place  the  knife 
obliquely.  Very  thin  sections  may  be  straightened  for 
mounting  by  floating  them  in  warm  water.  The  slide  pre- 
pared with  Mayer's  albumen  (See  p.  25)  is  then  dipped  be- 
neath them,  and  if  carefully  lifted,  the  section  rests  smoothly 
in  place  thereon. 

Celloidin  blocks  are  treated  differently.  The  knife  is  placed 
obliquely  and  kept  moist  with  80  per  cent,  alcohol.  The  block 
likewise  is  kept  moist,  and  as  the  sections  are  cut,  they  are 
transferred,  by  means  of  a  large  sable  brush,  to  a  dish  of  the 
same  alcohol,  and  allowed  to  remain  there  until  required.  If 
the  celloidin  is  too  soft,  the  sections  will  be  quite  thick.  This 
may  be  remedied  by  hardening  the  blocks  in  alcohol  contain- 
ing I  to  5  per  cent  of  glycerin.  Celloidin  answers  very  well 
for  the  nervous  system,  but  where  thin  sections  are  desired, 
the  paraffin  method  is  preferable. 


DECALCIFICATION.  II 

DECALCIFICATION. 

Bone  and  teeth  may  be  ground  for  study.  If  sections 
are  desired,  the  inorganic  matter  must  be  removed,  by  means 
of  acids.    This  process  is  Decalcification. 

Whole  teeth  and  small  pieces  of  bone  are  fixed  and  hard- 
ened in  solutions  containing  a  salt  of  chromium,  and  are  al- 
lowed to  remain  as  long  as  required.  After  being  thoroughly 
washed  and  dehydrated  as  above,  they  are  ready  for  the  de- 
calcifying agent,  of  which  large  quantities  are  to  be  used. 
The  solutions  given  below  are  the  most  important. 

I.  Phloroglucin-Nitric  Acid  is  no  doubt  the  best.  It 
consists  of 

Phloroglucin *    .      .     .         i  gm. 

Nitric   acid    (concentrated) 5  c.c. 

Alcohol  (70  per  cent.) 100  c.c. 

The  phloroglucin  is  dissolved  in  the  nitric  acid,  and  al- 
lowed to  stand  until  the  fumes  have  disappeared  (about 
twenty-four  hours).  The  alcohol  is  then  added,  and  the  so- 
lution is  ready  for  use.  The  teeth  or  bone  are  placed  therein 
until  readily  penetrated  by  a  needle  or  cut  with  a  scalpel.  The 
tissues  are  then  transferred  to  alcohol  and  dehydrated  in  the 
manner  already  stated.  Celloidin  is  the  better  infiltrating 
agent,  as  heat  tends  to  harden  osseous  tissues.  Additional 
nitric  acid  may  be  added  if  desired,  but  not  over  20  per  cent. 

Mayer's  Solution  is  a  5  per  cent,  solution  of  nitric  acid 
in  95  per  cent,  alcohol.  It  acts  very  well.  The  alcohol  is  sup- 
posed to  prevent  swelling  of  the  tissues. 

Trichloracetic  Acid.  A  5  per  cent,  solution  of  this  is  used. 
It  is  slower  than  the  nitric  acid,  but  the  treatment  is  the  same. 

Staining.  In  order  to  study  the  various  portions  of  a 
cell,  they  must  be  differently  stained.  Two  stains  are  gen- 
erally  used — NUCLEAR,    or   basic;    and,   protoplasmic,    or 


12  TECHNIC. 

ACID.  The  NUCLEAR  stain  is  used  first,  followed  by  the  acid  ; 
this  is  called  counter-staining.  Gruebler's  products  are 
recommended. 

Basic  Stains.  The  most  important  of  the  basic  stains  are 
HEMATOXYLIN  and  the  anilin  dyes. 

There  are  several  ways  to  prepare  the  hematoxylin.  The 
most  rapid  is  the  Harris  method. 

Hematoxylin  (harris). 

Hematoxylin I  gm. 

Absolute     alcohol lO  c.c. 

Potassium  alum   (sat.  aq.  sol.)    .      .      .      .      .     200  c.c. 

Dissolve  the  hematoxylin  in  the  alcohol  and  add  it  to  the 
alum  solution.  When  this  is  brought  to  a  boil,  add  i  gm.  of 
mercuric  oxid,  and  cool  the  solution  rapidly.  The  oxygen 
liberated  ripens  the  solution  immediately,  and  the  stain  is 
ready  for  use  when  cool.  It  should  be  filtered  and  diluted 
with  three  to  four  times  the  quantity  of  water,  when  ready, 
and  will  require  three  to  five  minutes  to  stain. 

Delafield's  hematoxylin  is  prepared  as  follows : 

Hematoxylin 4  gms. 

Alcohol 25  c.c. 

Ammonium  alum  (sat.  aq.  sol.) 400  c.c. 

Dissolve  the  hematoxylin  in  the  alcohol,  and  add  this  solu- 
tion, drop  by  drop,  to  the  alum  solution.  Expose  this  to  the 
light  and  air  for  a  week  or  more,  and  then  filter.  To  the 
filtrate  add 

Glycerin 100  c.c. 

Methyl  alcohol 100  c.c. 

Expose  again  for  a  long  time,  and  filter.  This  solution 
must  be  diluted  three  to  four  times,  like  Harris'. 


STAINS.  13 

Acid  hematoxylin  is  made  up  as  follows : 

Hematoxylin I  gm.  . 

Absolute    alcohol 30  c.c. 

Glycerin 60  c.c.  \  Saturated 

Water 60  c.c.  \  with  alum. 

Glacial  acetic  acid 3  c.c. 

Add  the  glycerin  and  water  to  the  hematoxylin,  dissolved 
in  the  alcohol ;  then  add  the  acid.  This  solution  must  be  ex- 
posed to  the  light  for  three  weeks,  when  it  becomes  bluish. 
Sections  stained  in  it  are  at  first  not  dark,  but  when  exposed 
to  the  light,  they  become  bluish. 

Most  of  the  ANiLiN  DYES  are  not  stable,  but  fade  when  ex- 
posed to  the  light. 

Methylene  blue  is  used  in  connection  with  the  nervous 
system. 

Methyl  green  is  used  for  organs  and  tissues  containing 
mucin,  and  in  blood  stains. 

Safranin  is  used  for  the  study  of  karyokinesis.  It  should 
be  used  upon  tissues  hardened  in  Flemming's  solution. 

Safranin *  i  gm. 

Absolute   alcohol       .........     100  c.c. 

Water 200  c.c. 

Sections  may  remain  in  this  solution  from  two  to  twenty- 
four  hours,  and  even  longer.  They  are  then  washed  in  plain 
alcohol,  or  carefully  differentiated  in  acid  alcohol,  and  then 
only  the  chromatin  retains  the  stain. 

BiSMARK  BROWN. — This  Stain  is  not  very  soluble  in  water. 
A  saturated  solution  is  made  by  boiling  the  stain  in  water, 
and  then  filtering.  This  gives  a  3  to  4  per  cent,  solution, 
which  is  diluted  by  adding  one-third  volume  of  absolute  alco- 
hol. This  stains  rapidly,  but  does  not  overstain.  It  is  usea 
to  advantage  in  contrast  with  hematoxylin,  hi  connective 
tissues  and  cerebellum.    It  answers  well  in  staining  the  acid 


14  TECHNIC. 

cells  of  the  stomach.  The  sections  should  first  be  deeply 
stained  with  hematoxylin,  and  then  subjected,  five  minutes, 
to  the  above  stain.  The  acid  cells  are  distinctly  brown,  while 
the  peptic  cells  have  a  bluish  cast. 

Acid  Stains. — The  more  comimon  acid  stains  are  eosin, 

PICRIC  ACID,  VAN  GIESON  and  ORANGE. 

EosiN  is  commonly  used  as  a  one  per  cent,  aqueous,  or  al- 
coholic solution.  It  requires  one  to  two  minutes,  and  should 
be  washed  ofif  with  water,  if  an  aqueous  solution  has  been 
used ;  otherwise,  with  alcohol. 

Picric  acid. — A  saturated  aqueous  solution  is  used  for 

15  to  30  seconds.  It  is  then  washed  quickly  with  95  per  cent 
alcohol. 

Van  GIESON  consists  of  picric  acid  and  acid  fuchsin. 

Picric  acid   (sat.  aq.  sol.) 100  c.c. 

Acid  fuchsin  (i  per  cent,  sol.) 5  c.c. 

Stain  from  one  to  three  minutes,  and  wash  with  alcohol. 
A  little  stronger  solution  is  used  for  the  nervous  system. 

Orange,  is  used  as  a  one  per  cent,  solution,  and  is  em- 
ployed as  a  blood  stain. 

There  are  stains  that  affect  both  nucleus  and  protoplasm 
sufficiently  to  differentiate  each  well.  Such  are  carmin  and 
CARMiNic  ACID  COMBINATIONS.  They  are  used  chiefly  in 
BULK  STAINING,  especially  for  entire  embryos. 

Borax  carmin  consists  of  carmin  boiled  in  a  solution 

OF  BORAX. 

Carmin 2  gms. 

Borax  (2  per  cent.  aq.  sol.) 200  c.c. 

Boil,  and  then  add  a  few  drops  of  a  five  per  cent,  solution 
of  acetic  acid  and  100  c.c.  of  70  per  cent,  alcohol.  After  a 
few  hours  filter,  and  to  the  filtrate  add  a  small  piece  of 
thymol  or  menthol,  to  preserve. 


STAINS.  15 

Allow  the  solution  to  stain  sections  for  15  to  20  minutes, 
and  then  differentiate  with  acid  alcohol,  prepared  as  follows : 

Hydrochloric  acid  (concentrated) i  cc. 

Water 29  cc. 

Alcohol    (95   per   cent.) 70  cc. 

This  stain  is  also  used  for  hulk  staining. 

2.  Alum    carmin. — This    is    prepared   by   boiling   one 

GRAM  OF  Cx\RMIN  with  IOC  CC.  OF  A  FIVE  PER  CENT.  SOLUTION 

OF  AMMONIUM  ALUM.     This  is  filtered  when  cool,  and  pre- 
served as  above.    It  also  requires  the  same  time  for  staining. 

3.  PiCRO-CARMiN  is  a  DOUBLE  STAIN,  and  its  preparation 
is  not  so  simple.    It  consists  of  the  following : 

Carmin .         4  gms. 

Ammonia    (concentrated)         10  cc 

Water 200  cc 

Dissolve  the  carmin  in  the  ammonia,  to  which  a  little  water 
has  been  added.  Then  add  the  water,  and,  after  24  hours, 
filter.  Allow  the  solution  to  stand  until  most  of  the  am- 
monia has  evaporated  and  add  an  aqueous  saturated  solution 
of  picric  acid  until  precipitation  occurs.  The  solution  must 
be  stirr€d  all  the  time.  Set  it  aside  to  crystallize  and  to  evap- 
orate to  one-third  of  its  bulk.  Pour  off  the  liquid  and  evap- 
orate it  to  dryness.  Dissolve  the  first  crystals  and  evaporate 
to  dryness.  This  residue,  as  a  one  per  cent,  solution  in 
water,  is  a  very  good  double  stain. 

Paracarmin    consists    of    carminic    acid^    aluminum 

CHLORID,  CALCIUM   CHLORID  and  JO  PER  CENT.   ALCOHOL. 

Carminic  acid i      gm. 

Aluminum   chlorid 0.5  gm. 

Calcium   chlorid 4     gms. 

Alcohol   (70  per  cent.) 100     cc 

Dissolve  and  filter. 


l6  TECHNIC. 

This  stain  is  especially  useful  in  embryology,  as  it  does 
not  overstain,  and  may  be  used  again  and  again.  It  is  a  good 
contrast  stain  to  Weigert"s  elastica  stain,  in  sections. 

Ehrlich-biondi-heidenhain  stain. — This  stain  is  used 
especially  in  blood  zvork  or  those  tissues  containing  many 
leukocytes.    It  is  composed  of  : 

Orange   (saturated  aq.  sol.) lOO  c.c. 

Acid  fuchsin  (saturated  aq.  sol.) 20  c.c. 

Methyl   green    (saturated   aq.    sol.)    ....       50  c.c. 

This  solution  is  diluted  to  make  a  solution  of  i-ioo,  which, 
upon  the  addition  of  acetic  acid,  must  be  bright  red.  It  is 
difficult  to  prepare,  and  so  is  better  bought  ready  for  use. 

Organs  should  be  fixed  in  corrosive  sublimate,  and  stained 
for  12  to  24  hours,  washed  with  90  per  cent,  alcohol,  and 
dehydrated  with  absolute  alcohol,  cleared  and  mounted  in 
balsam. 

Besides  these,  there  are  special  stains,  by  means  of  which, 
certain  structures  are  brought  out.  Among  these,  the  most 
important  are  the  Gold,  Silver,  Myelin  and  Elastica  Stains. 

The  Gold  Stain,  used  for  lymphatic  spaces  and  nerve  end- 
ings, is  not  always  successful ;  but  when  it  succeeds,  the  re- 
sults are  beautiful  and  gratifying.  There  are  a  number  of 
ways  of  preparing  the  solution,  but  the  best  is  the  boiling 
method. 

Eight  c.c.  of  a  one  per  cent,  solution  of  gold  chlorid  are 
mixed  with  two  c.c.  of  formic  acid,  and  brought  to  a  boil,  and 
cooled.  This  is  repeated  three  times,  and  it  is  then  ready  for 
use.  Small  strips  (3  to  5  mm.  thick)  are  placed  in  it  for 
one  hour,  and  the  container  kept  in  the  dark.  They  are  then 
washed  in  distilled  water,  and  exposed  to  the  light  in  a  solu- 
tion of  formic  acid  (loc.c.  of  acid  to  40  c.c.  of  water)  for  one 


SPECIAL    STAINS.  1 7 

or  two  days.     They  are  then  dehydrated  in  70  per  cent,  al- 
cohol, and  left  there  for  4  to  8  days  or  longer. 

Silver  Nitrate. — Pieces  of  the  nervous  system  are  fixed 
in  the  Golgi  solution  (see  Fixatives,  p.  3)  and  then  placed 
in  silver  nitrate.     The  steps  are  as  follows : 

Half-inch  cubes  of  the  nervous  system  are  fixed  in  the 
dark  for  three,  five  and  seven  days  in  Golgi's  solution,  which 
is  to  be  renewed  once  after  the  first  two  or  three  hours.  The 
tissues  are  then  washed,  for  one  minute,  in  distilled  water, 
blotted  between  filter  paper  and  transferred  to  a  0.75  per 
cent,  solution  of  silver  nitrate  for  two  to  four  days.  While 
in  this  solution,  they  are  exposed  to  the  light.  They  are  then 
removed  to  absolute  alcohol  for  two  to  three  hours,  dried 
for  one  minute  between  filter-paper,  cleared  in  toluol,  cast 
in  parafiin  and,  when  cold,  cut  with  a  flooded  knife,  as  in 
the  celloidin  technic. 

The  results  seem  as  good  if  the  dehydration  be  prolonged 
to  six  or  eight  hours  and  the  tissues  then  cleared,  over  night, 
in  pure  cedar  oil,  and  finally  infiltrated,  for  six  to  eight  hours^ 
in  the  parafiin  bath.  The  blocks  cut  much  better,  and  they 
may  be  preserved  indefinitely. 

By  using  3,  5  and  7  days  for  fixation,  dififerent  blocks  are 
prepared,  of  which  some  will  be  successful. 

Silver  nitrate  is  used  chiefly  for  nervous  tissues.  It  may 
also  be  injected  into  the  blood  vessels  to  stain  the  en- 
dothelium, and  into  the  lymphatics  to  outline  the  small  chan- 
nels. It  has  also  been  used  in  the  liver,  to  outline  the  bile 
capillaries. 

Myelin  Stain. — This  is  w^eigert's  hematoxylin  stain 
FOR  myelin  sheaths.  The  tissues  are  fixed  in  bichromate, 
though  this  is  not  absolutely  necessary.  Celloidin  infiltration 
is  usually  the  best. 


l8  TECHNIC. 

After  the  sections  have  been  cut,  they  are  placed,  for 
twenty-four  hours,  in  the  following  solution : 

Potassium  bichromate 5  gms. 

Chrom    alnm 2  gms. 

Water 100  c.c. 

They  are  then  washed  thoroughly,  and  transferred  to  the 
following  solution,  for  twenty-four  hours : 

Copper    acetate 5     gms. 

Acetic  acid  (36  per  cent.) 5     c.c. 

Chrom    alum 2.5  gms. 

Water 100     c.c. 

This  solution  is  a  mordant.  The  sections  are  carefully 
washed  and  carried  into  the  following  solution : 

Hematoxylin i  gm. 

Absolute  alcohol 10  c.c. 

Lithium  carborate  (sat.  aq.  sol.) i  c.c. 

Water .90  c.c. 

The  sections  are  stained,  from  fifteen  minutes  to  two  or 
four  hours,  in  this  solution,  and  then  washed  until  the  wash- 
ings are  clear.    They  are  then  differentiated  in  the  following : 

Potassium   ferricyanid 5  gms. 

Borax        4  gms. 

Water        200  c.c. 

In  this  solution  they  must  remain  vmtil  the  gray  matter 
becomes  yellowish.  This  change  must  be  watched  under  the 
microscope.  The  sections  are  immediately  transferred  to 
water,  which  is  frequently  renewed.  They  are  then  dehy- 
drated, cleared  and  mounted  in  balsam. 

The  myelin  sheaths  will  be  bluish  black. 


CLEARING    AGENTS.  I9 

Weigert's  Elastica  Stain  is  used  to  demonstrate  the  elas- 
tic TISSUE  in  organs  and  tissues,  and  is  prepared  as  follows : 

Fuchsin ...         2  gms. 

Resorcin 4  gms. 

Water         200  c.c. 

This  mixture  is  brought  to  a  boil,  and  then  25  c.c.  of  a  solu- 
tion of  liquor  ferri  sesquichlorati  added,  the  mixture  stirred 
and  boiled  for  3  to  5  minutes.  When  cool,  it  is  filtered,  and 
the  precipitate  dissolved  upon  the  filter,  in  200  c.c.  of  95  per 
cent,  alcohol.  This  is  stirred  and  boiled  until  the  precipitate 
is  entirely  dissolved.  The  solution  is  then  cooled  and  brought 
up  to  200  c.c.  with  95  p^r  cent,  alcohol  and  4  c.c.  of  hydro- 
chloric acid  added. 

Sections  should  be  stained,  from  20  minutes  to  an  hour,  in 
this  solution,  washed  well  in  95  per  cent,  alcohol,  cleared 
and  mounted. 

CLEARING  AGENTS  FOR  SECTIONS. 

After  staining  and  dehydrating,  the  sections  are  to  be 
CLEARED  (See  Slide  Technic,  p.  27).  The  clearing  agent 
removes  the  alcohol  and  prepares  the  section  for  the  final 
step  of  mounting.  These  agents  differ  from  those  used  in 
block  technic.  When  balsam  or  dammar  is  to  be  used,  the 
sections  are  cleared  with  an  oil.  Of  these,  the  following  are 
the  most  important: 

Creosote  (beechwood)  is  one  of  the  commonest  and  the 
best  for  general  laboratory  use. 

Oil  of  origanum  is  also  a  very  useful  clearing  agent,  and 
is  especially  adapted  for  celloidin  sections  and  those  stained 
with  van  Gieson's  stain.  It  neither  dissolves  the  celloidin 
nor  renders  it  stiff. 

Oil  of  cloves  acts  rapidly,  but  dissolves  celloidin  and  re- 


20  TECH  NIC. 

moves  anilin  dyes.  It  does  not  evaporate,  but  renders  the 
section  hard  and  becomes  yellow  with  age. 

Cedar-wood  oil  clears  slowly,  but  has  the  advantage  of 
not  abstracting  the  anilin  dyes. 

Oil  of  bergamot  is  very  good,  but  has  the  disadvantage 
of  removing  eosin. 

Xylol,  toluol,  benzol  all  act  very  rapidly,  and  require 
dehydration  with  absolute  alcohol.  They  are  useful  with 
anilin  stains,  and  are  readily  applicable  as  solvents  of  balsam. 
They,  however,  render  celloidin  stif¥  and  hard. 

Carbol-xylol  is  a  mixture  of  xylol  and  carbolic  acid. 

Xylol I  part. 

Carbolic  acid -      -     3  parts. 

It  acts  very  rapidly,  and  is  best  for  hematoxylin  and  carmin 
stains ;  it  does  not  stiffen  celloidin. 

Anilin  oil-xylol  consists  of  anilin  oil,  tzvo  parts,  and 
XYLOL,  one  part.  It  is  more  commonly  used  than  the  pre- 
ceding. 

Most  of  the  oils  require  about  ^ve  minutes  to  act.  The  sec- 
tions are  set  aside  during  this  time.  In  the  case  of  rapidly- 
acting  agents,  the  slides  are  retained  in  the  hand  and  rocked 
back  and  forth  until  the  section  is  clear.  This  is  usually  ac- 
complished in  a  minute  or  so. 

After  clearing,  the  sections  are  ready  for  the  final  step, 
that  of  MOUNTING.  There  are  a  number  of  mounting  media. 

such  as  BALSAM,  DAMMAR,  FARRANt's  SOLUTION  and  GLYCER- 
IN JELLY. 

Balsam. — Sections  to  be  mounted  in  balsam  must  be 
thoroughly  dehydrated  and  cleared  in  an  oil.  The  oil  is  then 
removed  by  blotting,  a  small  drop  of  balsam  placed  upon  the 
specimen  and  a  clean  cover-glass  applied. 


INJECTION  21 

The  balsam  is  soluble  in  chloroform,  Hirpentine,  benzol  or 
xylol.  The  latter  agent  is  the  best.  Sections  mounted  in 
this  medium  are  permanent. 

Dammar  is  more  complex.     It  consists  of  the  following: 

Gum  dammar i^  oz. 

Gum    mastic ^  oz. 

Turpentine         2      oz. 

Chloroform 2      oz. 

The  dammar  is  to  be  dissolved  in  the  turpentine,  and  the 
mastic  in  the  chloroform.  Each  is  to  be  filtered,  the  filtrates 
mixed  and  the  mixture  filtered.  This  is  to  be  kept  in  a  well- 
stoppered  bottle,  to  prevent  the  evaporation  of.  the  chloro- 
form. 

Farrant's  solution. — Sections  to  be  mounted  in  this 
medium  are  neither  dehydrated  nor  cleared,  but  washed  with 
water  and  mounted  in  this  solution.  It  is  prepared  by  adding 
gum-arabic  to  a  mixture  of  equal  parts  of  water,  glycerin 
and  a  saturated  solution  of  arsenious  acid.  The  solution 
must  be  filtered  after  the  gum  is  dissolved,  and  should  have 
the  consistence  of  a  thick  syrup. 

Preparations  mounted  in  this  medium  may  be  made  per- 
manent by  ringing.  This  is  done  by  running  a  ring  of  ce- 
ment around  the  edge  of  the  cover-glass. 

Glycerin  Jelly. — This  medium  must  be  warmed  before  it 
can  be  used.  A  drop  is  placed  upon  the  specimen,  and  the 
cover-glass  quickly  applied,  as  this  medium  sets  rapidly.  It 
is  used  for  special  purposes,  as  for  isolated  cells,  urinary 
caists,  crystals,  etc.  Neither  dehydration  nor  clearing  is 
necessary. 

INJECTION. 

Injection  masses. — In  order  to  study  the  circulatory 
system,  the  vessels  must  be  injected  with  a  substance  that 
will  outline  them.  For  this  purpose,  either  an  aqueous  sohi- 
tion  of  Berlin  blue,  or  gelatin  masses  are  used. 


22  TECHNIC. 

Berlin  blue  is  used  in  water,  one  part  to  20,  and  this  is 
injected  with  a  hand  syringe  or  by  continuous  air  pressure. 
It  gives  very  good  results. 

The  GELATIN  MASSES  may  be  either  carmin  or  Prussian 

BLUE. 

The  CARMIN  mass  consists  of  the  following: 

Carmin 2  gms. 

Water. 
Ammonia.     . 

Stir  the  carmin  in  a  little  water,  and  add  strong  ammonia, 
drop  by  drop,  until  the  carmin  is  entirely  dissolved.  Filter 
the  solution  and  add  it  carefully  to  the  melted  gelatin.  The 
latter  is  prepared  by  soaking  gelatin  in  double  its  quantity  of 
water,  and  melting.  The  mixture  is  stirred  and  then  neu- 
tralized with  dilute  acetic  acid.  If  too  acid,  the  carmin  will 
be  precipitated,  and  if  the  ammonia  is  not  neutralized  and 
the  gelatin  is  quite  alkalin,  the  stain  will  not  be  limited  to  the 
injected  vessels,  but  will  be  diffused  into  the  surrounding 
tissues. 

This  mass  should  be  filtered  while  hot,  and  preserved 
with  a  little  camphor. 

The  PRUSSIAN  BLUE  mass  is  somewhat  similar.  Four 
gms.  of  the  Prussian  blue  are  stirred  into  80  c.c.  of  water,  and 
the  mixture  added  to  gelatin  prepared  as  above.  The  solu- 
tion is  filtered  while  hot,  and  preserved  with  camphor,  or 
covered  with  methyl  alcohol. 

The  entire  body,  or  individual  organs,  may  be  injected. 
When  the  hand  syringe  is  used,  great  care  must  be  exercised 
that  the  pressure  be  not  too  great,  as  the  vessels  will  rupture 
and  the  mass  extravasate.  The  continuous  air  pressure 
method  is  the  better.  The  mass  must  be  melted  and  the  ani- 
mal kept  warm  by  immersion  in  warm  water.  As  soon  as 
the  injection  is  complete,  the  animal  or  organ  is  immersed 


BLOOD.  23 

in  ice- water,  so  that  the  gelatin  may  set  immediately.  When 
the  body  is  cooled,  the  organs  are  cut  into  blocks,  and  trans- 
ferred to  80  per  cent  alcohol,  where  they  remain  until  thor- 
oughly hardened,  which  takes  from  one  to  three  days.  They 
are  then  treated  with  95  per  cent,  alcohol  to  dehydrate, 
cleared  and  infiltrated  like  any  other  tissue. 

Blood  is  drawn  from  the  finger  tip  or  lobe  of  the  ear.  The 
part  is  thoroughly  cleansed  and  finally  washed  with  alcohol. 
A  sterilized  needle  is  then  plunged  to  a  depth  of  about  one- 
eight  of  an  inch,  and  the  blood  allowed  to  flow.  The  part 
should  not  he  squeezed,  as  this  dilutes  the  blood  with  lymph, 
and  causes  errors  in  accurate  work. 

Blood  spreads  are  obtained  by  touching  a  drop  of 
blood  with  a  cover-glass,  and  immediately  placing  this 
upon  a  second  glass.  The  two  are  then  slid  apart,  so  that  a 
thin  Hhn  of  blood  is  present  upon  each.  If  the  glasses  are 
lifted  apart,  the  cells  are  greatly  distorted  and  useless  for 
study.  The  spreads  are  allowed  to  dry  in  the  air,  and  then 
fixed  by  (i)  heat,  (2)  alcohol-ether  mixture,  or  (3) 
the  alcohol-formalin  solution. 

If  HEAT  is  used,  the  spreads  are  placed  in  an  oven,  and 
kept  at  a  temperature  of  120°  C.  for  twenty  minutes. 

The  ALCOHOL-ETHER  MIXTURE  consists  of  equal  parts  of 
absolute  alcohol  and  ether.  This  fixes  the  spreads  in  twenty 
minutes.     Results  with  this  fixative  are  very  good. 

The  ALCOHOL-FORMALIN  MIXTURE  consists  of  ninc  parts 
of  absolute  alcohol  and  one  part  of  formalin.  Spreads  are 
fixed  in  twenty  minutes. 

After  fixation,  the  spreads  are  allowed  to  dry,  and  may 
then  be  stained  like  any  other  tissue.  Hematoxylin  and  eosin 
give  a  good  result. 

Among  special  stains  is  the  ehrlich-biondi-heidenhain 
stain.    For  its  composition,  see  Stains,  p.  16. 


24  TECHNIC. 

Wright's  blood  stain  is  one  of  the  most  satisfactory, 
and  is  prepared  in  the  following  manner : 

Steam  1.5  grams  of  methylene  blue  in  150  ex.  of  a  one  per 
cent,  aqueous  solution  of  sodium  bicarbonate  for  one  hour,  in 
a  sterilizer.  Add  a  one-tenth  per  cent,  aqueous  solution  of 
yellowish  eosin  to  100  c.c.  of  the  methylene  blue  solution 
until  the  mixture  turns  purple,  and  a  yellowish  metallic  scum 
forms  upon  the  surface,  and  a  blackish  precipitate  appears ; 
about  500  c.c.  of  eosin  solution  will  be  required,  and  it  should 
be  added  slowly,  while  constantly  stirring.  The  solu- 
tion is  then  filtered,  the  precipitate  dried  and  made  into  a 
saturated  solution  with  methyl  alcohol.  This  solution  is 
filtered  and  80  c.c.  of  the  filtrate  are  diluted  with  20  c.c.  of 
methyl  alcohol. 

Dried  spreads  are  stained,  for  one  minute,  with  this  solu- 
tion, and  the  stain  then  diluted  upon  the  glass,  with  water, 
until  the  stain  is  semi-transparent.  After  two  or  three  min- 
utes, the  spreads  are  thoroughly  washed  with  distilled  water, 
dried  quickly  and  mounted.  The  acidophilic  granules  are 
reddish  lilac  and  red,  while  the  basophilic  granules  are  deep 
blue,  or  even  black. 

This  solution  both  Hxes  and  stains  the  cells. 

Eosin  and  methylene  blue  give  good'  results.  The 
spreads  are  stained  in  a  one-half  per  cent,  alcoholic  solution 
of  eosin  for  two  or  three  minutes,  using  gentle  heat.  Then 
they  are  placed  in  a  saturated  aqueous  solution  of  methylene 
blue  for  two  or  three  minutes.  The  spreads  are  then  thor- 
oughly washed,  dried  and  mounted  in  balsam.  As  a  rule, 
the  granules  of  the  leukocytes  are  well  stained. 

In  order  to  obtain  the  hell-sMped  red  cells,  the  finger 
should  be  thoroughly  cleansed,  and  the  blood  drawn  as  usual. 
The  first  drop  should  be  wiped  off  and  a  drop  of  one  per  cent, 
osmic  acid  solution  placed  over  the  puncture.  The  blood  then 


SLIDE   TECHNIC.  2^ 

flows  into  the  osmic  acid,  which  acts  as  a  fixative,  and  pre- 
vents contact  with  the  air  until  fixation  is  complete.  If  this 
drop  be  examined  under  the  microscope,  the  bell-shaped 
cells  will  be  seen  in  great  numbers. 

Blood  platelets  may  also  be  stained  in  the  above  way. 

Erythroblasts  of  the  spleen  may  be  studied  in  spreads 
made  by  drawing  thin  pieces  of  the  organ  over  cover-glasses. 
These  are  then  fixed  in  the  following : 

Mercuric   chlorid 78  gm. 

Sodium    chlorid .28  gm. 

Water 30       c.c. 

This  solution  should  be  filtered,  and  spreads  fixed  in  it  for 
one  minute.  They  should  then  be  washed  and  stained  one- 
half  hour  with  aqueous  hematoxylin,  washed  and  covered 
with  a  3  per  cent,  solution  of  eosin,  for  two  to  three  minutes. 
They  are  then  washed,  dried  and  mounted. 

Spreads  may  be  stained,  for  three  minutes,  with  eosin,  and 
one-half  minute  with  five  per  cent,  methylene  blue,  then 
washed,  dried  and  mounted. 

Slide  Technic. — The  preparation  of  sections  for  micro- 
scopic study  requires  skill  and  care. 

Paraffin  sections  are  made  to  adhere  to  the  slide  by  means 
of  Mayer's  albumen.  This  is  prepared  by  mixing,  thor- 
oughly, white  of  egg  and  glycerin  in  equal  parts,  and  filter- 
ing.   A  very  thin  film  is  all  that  is  necessary. 

The  following  desk  reagents  are  sufficient  for  all  ordinary 
work: 

Coplin  staining  jar,  containing  lodin. 

Coplin  staining  jar,  containing  Kerosene. 

Coplin  staining  jars,  containing  Alcohol,  Nos.  i  and  2. 

One  Barnes  bottle,  containing  Hematoxylin. 

One  Barnes  bottle,  containing  Van  Gieson's  stain. 

One  Barnes  bottle,  containing  Eosin. 


26  TECHNIC. 

One  Barnes  bottle,  containing  Alcohol. 
One  Barnes  bottle  containing  Water. 
One  Barnes  bottle  containing,  Acid  Alcohol. 
One  Barnes  bottle,  containing  Creosoie. 
One  Barnes  bottle,  containing  Albumen. 
One  Barnes  bottle,  containing  Picric  Acid. 

The  method  of  procedure  for  staining  is  given  in  detail 
below : 

1.  Cover  a  clean  slide  with  a  thin  film  of  albumen. 

2.  Add  a  few  drops  of  water,  and  float  on  this  the  cut 
paraffin  section. 

3.  Warm  gently  over  a  flame,  so  as  to  spread  the  section, 
but  be  careful  not  to  melt  the  paraffin. 

4.  Drain  and  set  aside,  or  in  an  oven,  for  six  to  twenty- 
four  hours.  The  slide  must  be  perfectly  dry  before  the  other 
step  can  be  carried  out.  Put  on  the  slide  an  identification 
label. 

5.  Place  in  the  kerosene  for  five  to  fifteen  minutes,  to 
remove  the  paraffin. 

6.  Wash  with  alcohol,  to  remove  the  kerosene,  and  place 
in  the  jar  of  iodin,  five  to  ten  minutes,  to  remove  the  crystals 
of  bichlorid  of  the  fixing  agent. 

7.  Remove  the  excess  iodin  from  the  slide  with  tissue 
paper,  wash  with  alcohol  and  place  in  the  iirst  alcohol  jar 
for  fifteen  minutes,  to  remove  the  remainder  of  the  iodin. 

8.  Drain  the  section,  wash  with  water,  cover  with  hema- 
toxylin for  three  to  five  minutes,  and  wash  with  water  to 
deepen  the  color. 

9.  Counter-stain.  Eosin  one  to  two  minutes,  wash 
with  water  and  then  alcohol,  to  remove  excess  stain ;  or, 

Van  Gieson  one-half  to  one  minute,  wash  with  water  and 
then  alcohol,  as  above ;  or. 

Picric  acid  fifteen  seconds  and  wash  with  alcohol. 


SLIDE   TECHNIC.  2^ 

Carmin  may  be  used  alone  for  fifteen  minutes,  or  followed 
by  picric  acid,  as  in  the  preceding. . 

ID.  After  washing  with  alcohol,  dehydrate  in  the  second 
jar  of  alcohol.    Allow  sections  to  remain  about  five  minutes. 

11.  Clean  the  slide  carefully  without  allozmng  the  sec- 
tion to  dry.     Blot  with  tissue  paper. 

12.  Cover  with  a  drop  or  two  of  creosote  for  five  min- 
utes. This  removes  the  alcohol,  renders  the  specimen  trans- 
parent, and  allows  the  use  of  balsam.  This  is  sectional  clear- 
ing. 

13.  Drain  off  the  creosote,  hlot,  add  a  drop  of  balsam  and 
cover  with  a  clean  cover-glass. 

14.  Remove  the  identification  Label,  apply  a  clean  one, 
and  write  the  name  thereon. 

After  the  paraffin  has  been  removed,  the  specimen  should 
never  he  allowed  to  dry. 

The  above  technic  will  answer  for  all  ordinary  histologic 
and  pathologic  work,  and,  if  strictly  adhered  to,  there  will 
not  be  the  slightest  trouble  in  making  excellent  preparations. 


CHAPTER  II. 


HISTOLOGY, 

Histology    is    the    science    that    treats    of    the    minute 

structure  of  normal  tissues  and  organs.     Although  to  the 

naked  eye  tissues  may  have  an  apparent  structure  that  seems 

ultimate,  when  examined  under  the  microscope  this  structure 

is  seen  to  be  but  gross.     Each  section  studied  will  be  found 

to  be  composed  of  minute  elements,  more  or  less  regular,  and 

definitely  grouped  and  arranged.     These  elements  are  Cells. 

A    Cell    is    a    small    mass    of    protoplasm    containing    a 

nucleus.     It  is  the  histologic  basis  of  the  body,  and  has  a 

^  A/^    complex  structure.     Certain  parts   are   absolutely  essential 

^5-%/^  for  the  proper  performance  of  its  various  functions,  while 

others  are  accessories,  which  most  cells  possess.     The  parts 

of  a  typic  cell  are : 

1.  Cell-body. 

2.  Nucleus.  ^ 

3.  Centrosome. 

4.  Nucleolus. 

5.  Cell-wall. 

I.  The  Cell-body,  or  Protoplasm,  or  Cytoplasm  is  a 
granular,  semi-solid  substance  that  constitutes  the  bulk  of  the 
cell.  It  may  or  may  not  be  limited  by  a  cell-wall.  It  consists 
of  two  main  parts,  the  Spongioplasm,  or  Filar-mass,  and 
the  Hyaloplasm,  or  Interfilar-mass. 

The  Spongioplasm,  as  its  name  indicates,  is  a  frame- 
work of  comparatively  solid  structure,  in  the  meshes  of  which 
is  found  the  semi-fluid  hyaloplasm.  The  elasticity  of  the 
spongioplasm  is  said  to  give  rise  to  ameboid  movements. 

In  the  protoplasm  are  to  be  seen  small  darkly-staining 
bodies,   the   microsomes,  and  paler  masses,   the   plastids. 

28 


THE   CELL 


29 


At  the  outer  margin  of  the  cell-body  is  a  narrow,  peripheral 
zone,  containing  no  microsomes,  known  as  the  Exoplasm. 
At  times,  there  are  other  structures  present,  as  fat  globules, 
glycogen,  secretion  granules,  vacuoles  and  pigment. 

The  cell-body  has  affinity  for  acid,  or  protoplasmic,  stains, 
such  as  eosin,  picric  acid,  carmin,  orange,  etc. 


Fig.   1. — Scheme  of  a  Cell.     Microsomes  and  spongioplasm  only  partly 
sketched   {St6hr's  Histology). 

1.  Spongioplasm  ;  2.  hyaloplasm  ;  3.  microsomes  ;  4.  exoplasm  ;  5.  chroma- 
tin ;  6.  achromatin  ;  7.  linin  ;  8.  chromatic  knots  ;  9.  nuclear  mem- 
brane ;  10.  centrosome ;  11.  nucleolus ;  12,  cell-membrane ;  13.  in- 
clusions. 


2.  The  Nucleus  is  usually  a  darkly-staining  body  having 
a  sharp  outline,  and  occupying,  as  a  rule,  a  central  position. 
In  glandular  cells,  its  location  varies  with  the  stage  of  secre- 
tory activity.  Its  structure  resembles  that  of  the  protoplasm, 
to  a  certain  extent.  It  consists  of  a  network  and  semi-fluid 
substance,  surrounded  by  a  distinct  membrane  or  wall. 


30  HISTOLOGY. 

The  network  is  called  the  chromatin,  or  nuclear  fibrils, 
and  the  semi-solid  substance,  the  nuclear  matrix,  sap,  or 

ACHROMATIN. 

Chromatin  is  the  part  of  the  nucleus  that  responds  to  the 
stains.  It  is  arranged  as  an  irregular  network  of  anastomos- 
ing fibrils,  each  consisting  of  a  delicate  central  thread,  the 
linin,  upon  which  the  real  chromatin  substance  is  arranged, 
in  the  form  of  granules.  It  is  the  most  important  portion 
of  the  nucleus  during  the  process  of  cell-division. 

Achromatin  is  the  semi-fluid  substance  that  fills  the 
meshes  of  the  chromatin.  It  reacts  but  faintly  to  stains,  and 
is  not  of  the  same  importance  as  the  above. 

The  nuclear  membrane  is  the  wall  that  limits  the  nucle- 
us. It  is  present  in  nearly  all  nuclei,  and  stains  readily.  It 
consists  of  amphipyrenin. 

Of  the  above  sfructures,  the  chromatin  persists  throughout 
all  the  stages  of  reproduction,  while  the  remainder  of  the 
nuclear  constituents  disappear. 

3.  The  Centrosome  is  a  small,  darkly-staining  structure, 
which,  owing  to  its  small  size,  has  been  found  in  but  few  of 
the  cells  of  the  human  body.  It  is  readily  seen  and  studied 
in  the  ova  of  some  of  the  lower  animals,  especially  those  of 
ascaris  megalocephala.  It  lies,  usually,  just  outside  of  the 
nucleus,  in  a  small,  clear  field  called  the  attraction  sphere, 
within  which  are  seen  delicate  lines  that  radiate  from  the 
centrosome.  The  attraction  sphere  and  the  centrosome  con- 
stitute the  astrosphere. 

Besides  being  the  center  of  cell- division,  the  centrosome 
seems  to  play  an  important  part  during  the  resting  stage.  In 
pigrnent  cells  and  white  blood  corpuscles,  it  seems  to  preside 
over  the  movements  of  the  whole  cell,  and  in  ciliated  and  flag- 
ellated cells  over  the  action  of  these  processes. 

4.  The   Nucleolus   is   a   small   body    found   within   the 


CELL  PROPERTIES  3 1 

nucleus.  It  is  not  always  present,  and  more  than  one  may 
be  found.  In  nerve  cells  and  ova  it  is  unusually  large  and 
readily  stained,  while  in  others  it  is  scarcely  noticeable.  Its 
importance  is  doubtful,  as  no  definite  function  has  as  yet 
been  found.  It  consists  of  pyrenin,  and  disappears  during 
cell-division.  .;       -tutc--^  %'-  '-  ^tr-^l-M^kyOc- 

5.  The  Cell-wall  is  a  more  or  less  prominent  m-embrane 
that  limits  cells.  It  is  not  present  in  all  animal  cells,  though  Lfejrl 
some  hold  that  even  the  wandering  cells  possess  a  delicate 
membrane.  In  some  instances,  it  consists  of  the  differenti- 
ated, peripheral  protoplasm,  and  in  others,  is  a  secretory  pro- 
duct of  the  protoplasm. 

Of  the  above  structures,  the  Cytoplasm,  Nucleus  and 
Centrosome  are  the  essential  parts,  when  the  important 
functions  of  the  cell  are  considered.  In  red  blood  cells,  the 
nucleus  is  absent,  and  as  a  consequence,  these  cannot  repro- 
duce themselves. 

Cells  differ  greatly  in  form  and  size ;  the  nucleus  conforms 
somewhat  to  the  shape  of  the  cell.    Usually,  but  one  is  pres-     ^ 
ent,  but  in  giant  cells  and  voluntary  striated  muscle,  many 
are  to  be  found.  [J^m-o^  uJ<L^^  '^, 

The  cell,  like  the  organism,  exhibits  a  number  of  proper- 
ties, such  as  Metabolism,  Growth,  Motion,  Irritability  and 
Reproduction. 

Metabolism  is  the  change  that  takes  place  in  a  cell  during 
the  performance  of  its  functions.  When  the  result  is  the 
formation  of  complex  structures,  the  process  is  called 
ANABOLiSM ;  if  destructive,  the  conversion  of  complex  to 
simple  compounds,  the  phenomenon  is  termed  katabolism. 
Secretion  and  excretion  are  anabolic  changes,  as  simple 
structures  are  converted  into  complex  compounds.  Secretion 
may  be  glandular  secretion,  or  simply  an  intercellular  sub- 
stance may  be  formed. 


32 


HISTOLOGY. 


Growth  is  the  result  of  an  anabolic  process.  The  cells  in- 
crease in  size,  equally  or  more  often  unequally,  depending 
upon  the  organ.  When  the  latter  occurs,  the  cell-form  is 
changed.  By  such  a  change  in  all  cells,  the  organism  in- 
creases in  size,  though  the  amount  contributed  by  each  cell 
may  be  microscopic. 

Motion.  But  few  cells  possess  this  property  to  any  great 
extent.  The  anieboid  leukocytes  show  it  best  as  they  may 
pass  from  one  part  of  the  body  to  another.    One  of  the  most 

'   rv  *  <v     Vv/:;yV-f/'*Cnromosomes.         Centrosome. 


j(y^ 


V 


Fig.  2.- 


-SCHEME  OF  THE  CLOSE   COIL  AND  THE   DIVISION   OP   THE 

Centrosomes    {Stohr's  Histology). 


4'Hv.i£#*rfcharacteristic  examples  of  this  property  is  exhibited  by  the 
^y  £«- ^ Aiuscles,  especially  the  voluntary  striated  variety.  Motion 
^V^''  '  niay  l>e  limited  to  only  a  portion  of  the  cell,  as  to  hair-like 
'^^  ,        processes  called  cilia. 

'''''•  ■  •    ^  Irritability  is  the  property  of  response  to  surrounding  in- 
fluences or  stimuli.    This  is  more  pronounced  in  the  individu- 


CCUlL 


^€^^-X'i^L 


^1  cells  of  such  animals  that  possess  no  nervous  system.  Here 


^j,    j'-    It  is  practically  a  primary  change  in  the  cell.    When  a  nerv- 
/y,,/'  ous  system  is  present,  this  presides  over  such  changes,  which 

/      ak*e  then  secondary, 
^if****      /^'AReproduction  is  the  process  by  means  of  which  a  cell  or 


CELL-DIVISION.  33 

an  organism  propagates  itself  and  continues  its  life  history. 
Without  this  or  an  analogous  process,  life  would  soon  cease 
to  exist.  It  is  of  two  varieties,  direct,  amitosis  or  budding 
and  indirect,  mitosis  or  karyokinesis.  Of  these,  the  latter 
is  the  more  common. 

In  Amitosis,  the  cell-body  is  m.arked  by  a  constriction 
that  gradually  deepens  and  is  imparted  to  the  nucleus.  As 
this  deepens,  the  protoplasm  and  nucleus  are  finally  divided 

Central  spindle. 


Fig.  3. — Scheme  of  the  Loose  Coil  and  Separation  of  the 
Centrosomes    {i^tohf's  Histology). 

into  two  small  but  practically  equal  cells,  which  have  the 
same  structure  as  the  parent  cell.  By  growth,  these  cells, 
which  are  called  daughter  cells,  increase  in  size,  until  that 
of  the  parent,  or  mother,  cell  is  attained. 

Mitosis  is  a  very  complex  process,  in  which  the  nucleus 
plays  a  very  important  part.  The  protoplasm  is  almost  pass- 
ive until  the  late  stages  of  the  process.  The  various  stages 
are  the  prophase,  metaphase,  anaphase  and  telophase. 
These  are  not  absolutely  separable  from  one  another.  The 
changes  that  occur  may  be  grouped  under  three  heads — 
nuclear,  centrosomic  and  protoplasmic. 


34  HISTOLOGY. 

Prophase. — The  nuclear  changes  are  quite  complex. 
Whereas  the  chromatin  is  ordinarily  arranged  as  an  irregular 
network,  when  division  begins  the  irregular  twigs  of  the  net- 
work gradually  become  smooth,  and  form,  usually,  a  single 
thin  closely-convoluted  thread,  called  the  close  spirem,  or 
SKEIN.  The  thread  becomes  thicker  and  shorter,  and  the 
coil  looser,  and  this  constitutes  the  loose  spirem,  or 
SKEIN.  The  thread  then  separates  into  a  number  of  segments 
called   CHROMOSOMES.      This   sometimes    occurs   before   the 

Polar  radiation.  Central  spindle. 


,«k*W^^^ 


Fig.  4. — Scheme  of  the  Mother  StAr,  or  Equatorial  Plate. 
( Stohr's  His  to  logy. ) 

loose  spirem  is  formed.  The  chromosomes  become  U  or  V- 
shaped,  and  arrange  themselves  along  the  equator  of  the  cell, 
with  the  closed  ends  directed  toward  a  common  center,  called 
the  polar  Held.  This  arrangement  is  termed  the  equatorial 
PLATE^  or  monaster,  and  practically  ends  the  chromatin 
changes  during  the  prophase. 

The  chromosomes  are  always  even  in  number,  and  the 
same  number  is  always  formed  in  each  cell  of  the  same 
species.    In  man,  the  number  is  said  to  be  sixteen. 

The  nuclear  membrane,  during  these  changes,  has  gradu- 
ally become  more  and  more  hazy,  and  finally  disappears. 
The  ackromatin  is  released,  and  mixes  with  the  protoplasm. 


KARYOKINESIS.  35 

The  nucleolus  likewise  gradually  fades  and  disappears. 

The  centrosome  is  the  dynamic  center  of  the  cell.  It  di- 
vides into  two  portions  (if  within  the  nucleus,  it  passes  first 
into  the  protoplasm),  each  oi  which  becomes  surrounded  by 
its  own  attraction  sphere.  These  centrosomes  gradually 
move  apart,  through  an  arc  of  90°,  to  opposite  poles  of  the 
cell.  During  this  change,  the  intervening  rays  remain  in 
contact,  forming  a  spindle  of  delicate  threads,  which  is  com- 
plete when  the  centrosomes  reach  their  polar  position.    This 


Fig.   5. — Scheme  of  Metakinesis,   Showing  the  Nuclear. Spindle. 
(Stohr's  Histology.) 

is  the  CENTRAL,  or  ACHROMATIC  SPINDLE,  and  the  threads  are 
of  the  utmost  importance,  and  become  attached  to  the 
chromosomes  of  the  equatorial  plate. 

With  the  formation  of  the  equatorial  plate  and  central 
spindle,  the  prophase  ends.  Variations,  too  numerous  to  de- 
scribe, occur,  but  the  above  is  the  usual  course  in  this  stage 
of  mitosis. 

Metaphase.  This  is  the  stage  during  which  the  chromo- 
somes divide  and  separate.  It  concerns  the  chromatin 
chiefly. 

The  chromosome  divide  longitudinally  into  two  equal  por- 
tions. This  cleavage  occurs  at  the  closed  end  first,  and  as  it 
proceeds,  the  daughter  chromosomes  become  separated,  one- 


36 


HISTOLOGY. 


half  being  drawn  toward  the  one  centrosome,  and  the  other 
toward  the  second.  This  gives  rise  to  a  second  spindle,  the 
NUCLEAR,  or  CHROMATIC  SPINDLE.  The  Separation  is  affected 
by  the  traction  exerted  upon  the  daughter  chromosomes  hy 
the  threads  of  the  central  spindle. 

Anaphase.  This  is  the  stage  of  complete  separation  of 
the  chromosomes.  The  latter  collect  around  their  respective 
centrosome,  and  remain  connected  to  the  opposite  set,  for 
some  time,  by  the  central  spindle  threads.  The  figures  thus 
formed  are  the  diasters,  or  daughter  stars. 


Fig.  6. — Scheme  of  the  Daughter 
Stars. 

{8t6hr's 


Fig.    7. — fecuEME    of    Division    of 
THE    Protoplasm    Forming 
Daughter  Cells. 
Histology.) 


Telophase.  This  stage  is  concerned  with  the  protoplas- 
mic changes  and  the  formation  of  a  resting  nucleus.  Up  to 
this  time,  the  protoplasm  has  been  practically  quiescent. 

The  chromosomes  collect  around  the  centrosomes,  and 
unite  to  form  a  close  skein.  Lateral  twigs  are  developed 
that  anastomose  to  form  the  nuclear  network,  a  nuclear  mem- 
brane is  formed  and  a  micleolus  appears. 

The  hitherto  inert  protoplasm  shows  changes.  A  double 
row  of  vaculoes  appears  at  the  equator  of  the  cell,  and  separa- 
tion occurs  in  the  intervening  space  until  two  separate  masses 
are  formed ;  these  are  the  daughter  cells. 


MATURATION.  37 

The  above  changes  are  usually  succeeded  by  a  period  of 
rest.  ^tc^ 

Although  apparently  a  long  process,  only  about  one-half  '■/•" 
hour  is  consumed  in  the  division  of  human  cells,  but  the  cells  . 
of  lower  animals  require  a  longer  period.  yii^ivl 

In  the  case  of  giant  cells,  the  nucleus  divides  and  redivides,  ^*^i 
while  the  protoplasm  remains  unchanged.     They  may  also 
be  formed  by  the  fusion  of  the  protoplasm  of  a  number  of 
cells  with  the  retention  of  the  individuality  of  the  nuclei. 

As  all  cells  are  developed  from  preexisting  elements,  it 
is  but  natural  that  the  original  cell  of  the  body,  the  Ovum, 
should  be  of  greatest  interest.  It  is  the  most  characteristic 
cell  of  the  body,  and  is  secreted  by  the  ovary.  It  is  the 
largest  cell,  and  illustrates  the  individual  parts  well. 

The  Ovum  consists  of  a  limiting  wall,  the  vitelline  mem- 
brane, that  is  well  developed.  Within  this,  is  the  protoplasm, 
vitellus,  which  consists  of  two  parts — the  deutoplasm,  or 
NUTRITIVE  YOLK,  and  the  animal  protoplasm,  or  forma- 
tive YOLK.  This  is  of  importance,  embryo  logic  ally.  Within 
the  vitellus  is  found  the  nucleus,  or  germinal  vesicle,  which 
contains  a  deeply  stained  nucleolus,  or  germinal  spot.  In 
what  might  be  termed  an  embryologic  ovnm,  there  are  two 
layers  external  to  the  vitelline  membrane,  the  zona  pellu- 
ciDA  and  the  corona  radiata.  Of  these,  the  former  is  the 
more  important,  because  of  the  part  which  it  plays  in  the 
early  stages  of  development. 

There  are  a  number  of  processes  that  occur  in  the  ovum 
before  it  can  develop  into  an  offspring.  Of  these,  the  most 
important  are  MATURATION  and  FERTILIZATION. 
The  former  occurs,  usually,  in  the  ovary,  and  the  latter,  as 
a  rule,  in  the  Fallopian  tube. 

Maturation  is  the  process  by  which  part  of  the 
chromatin  and  a  small  portion  of  the  protoplasm  are  ex- 


38 


HISTOLOGY. 


traded  in  the  form  of  two  minute  structures  called  polar 
BODIES.  It  is  a  modified  karyokinesis,  and  its  object  is  un- 
known. All  ova  must  pass  through  this  process  before  they 
can  be  fertilized. 

Fertilization  is  the  process  in  which  the  male  and 
female  elements  unite  to  form  a  complete  and  perfect  cell, 
which,  by  division,  gives  rise  to  the  cells  that  ultimately  form 
the  whole  body. 


Ovum  from  a  Cow. 


Corona   radiata ;    2.   zona  pellucida :    3.   vitellus ;   4.    germinal   vesicle; 
5.  germinal  spot    (Stohr's  Histology). 


The  male  element,  or  spermatozoon  consists  of  head, 
MIDDLE-PIECE  and  TAIL.  Of  thcsc  the  HEAD  and  middle- 
piece,  representing  the  nucleus  and  centrosome,  respec- 
tively, of  a  cell  of  the  testicle,  enter  the  ovum  and  form  eight 
chromosomes.  The  chromatin  of  the  germinal  vesicle  of 
the  ovum  also  forms  eight.  By  longitudinal  cleavage  thirty- 
two  are  formed  of  which  sixteen  enter  into  each  diaster  and, 
consequently,  each  daughter  cell.     By  this  process  the  de- 


DERIVATIVES  OF  THE  TRIPLOBLAST.  39 

scendants  of  the  fertilized  ovum  contain  double  the  number 
of  chromosomes  that  existed  in  either  of  the  original  cells 
before  fertilization. 

After  fertilization  the  ovum  divides  and  redivides  forming 
an  irregular  mass  of  cells  called  the  Morula,  or  Mulberry 
Mass.  Certain  of  these  cells  form  a  complete  layer  that  sur- 
rounds the  remainder,  which  constitutes  an  irregular  mass. 
The  layer  is  the  Outer  Cell-mass  and  the  latter  the  Inner 
Cell-mass.  This  structure  constitutes  the  Blastula,  or  one- 
layered  vesicle.  Of  these  two  structures  the  inner  is  the 
more  important  as  it  persists  and  forms  the  whole  body 
while  the  outer  disappears. 

The  Inner  Cell-mass  forms  two  layers,  an  outer,  several 
cells  in  thickness,  the  Ectoderm,  or  Epiblast,  and  an  inner, 
composed  of  but  a  single  layer,  the  Entoderm,  or  Hypo- 
blast This  is  the  Gastrula,  or  Diploblast.  The  ecto- 
derm and  entoderm  each  set  aside  a  number  of  cells  which 
by  multiplication  form  a  third  layer,  the  Mesoderm,  or  Me- 
SOBLAST,  that  lies  between  the  two.  This  structure  receives 
the  name  of  Blastodermic  Vesicle,  or  Triploblast. 

From  these  three  primitive  layers  all  the  organs  and  tis- 
sues of  the  body  are  formed  as  follows  : 

Ectoderm. 

The  nervous  system  (cerebro-spinal  and  sympathetic)  the 
retina,  the  bulk  of  the  crystalline  lens,  the  epithelium  of  the 
cornea  and  conjunctiva,  the  epithelium  of  the  internal  ear 
and  of  the  olfactory  organ. 

The  epithelial  lining  of  the  anterior  portion  of  the  male 
urethra,  the  vestibule  and  labia  of  the  female  and  the  glands 
leading  thereto. 

The  epithelial  lining  of  the  mouth  and  salivary  glands, 
the  enamel  of  the  teeth,  the  cells  of  the  nasal  tract,  to  the 
pharynx,  and  its  glands  and  the  lining  of  the  anus. 


40  HISTOLOGY. 

The  epidermis  and  appendages  of  the  skin. 

Entoderm. 

The  epithehal  lining  of  the  bladder,  of  the  first  portion 
of  the  male  and  entire  female  urethra  and  the  prostate. 

The  epithelium  of  the  tongue,  thymus  and  thyroid  bodies 
of  the  parathyroids,  middle  ear  and  Eustachian  tube. 

The  epithelium  of  the  alimentary  and  respiratory  tracts 
from  the  mouth  and  posterior  nares  down  and  the  epithelium 
of  all  glands  opening  into  these  structures. 

Mesoderm. 

The  vascular  system. 

The  lymphatic  system  including  the  large  serous  cavities, 
spleen  and  thymus  body  (except  the  corpuscle^  of  Hassal). 

The  muscular  system  (except  the  muscles  of  the  sweat- 
glands). 

The  connective  tissues. 

Testicle,  vas,  seminal  vesicles,  ejactulatory  duct,  ovary, 
Fallopian  tubes,  uterus  and  vagina. 

Kidneys  and  ureters. 


CHAPTER  III. 


THE  TISSUES. 

From  the  preceding  table  it  will  be  seen  that  all  tissues 
are  developed  from  the  three  layers  of  the  triploblast.  These 
tissues  are  grouped,  histologicallyj  under  four  classes,  Epi- 
thelial, Connective,  Muscular  and  Nervous. 

A  Tissue  consists  of  similarly  differentiated  cells  held  to- 
gether by  intercellular  cement, "  and  performing  a  definite 
function.  The  intercellular  substance  varies  with  the  differ- 
ent tissues.  The  cells  of  a  tissue  may  be  so  arranged  as  to 
form  an  organ  or  merely  a  supporting  structure. 

EPITHELIUM. 

The  Epithelial  Tissues  are  characterized  by  the  small 
amount  of  the  intercellular  cement.  The  cellular  elements 
are  usually  prominent,  and  rich  in  granular  protoplasm. 
They  are  found  lining  cavities  that  communicate  normally 
with  the  air  and  usually  secrete,  although  they  may  also  have 
a  protective  function.  The  cells  vary  in  size,  form  and 
arrangement,  as  will  be  seen  later. 

For  convenience  of  description,  the  cells  are  classified  as 


ows: 

.i:f:^ 

I.     Squamous. 

4. 

Prickle  cells. 

a.     Simple. 

5. 

Goblet  cells. 

b.     Stratified. 

6. 

Trasitional  cells. 

2.     Columnar. 

7. 

Pigmented. 

c.     Simple. 

Specialized. 

d.     Stratified. 

8. 

Neuro-epithelial. 

Modified. 

9- 

Glandular. 

3.     Ciliated. 

e.     Simple. 

f.     Stratified. 

41 


42 


THE  TISSUES. 


I.  Squamous,  a.  The  simple  squamous  cells  consist 
of  a  single  layer  of  flattened  elements,  each  containing  a 
large  nucleus.    This  is  usually  in  the  center,  and  has  an  oval, 


>]  9\  ®\  (&[  &\ 


Fig.   9. 
a.    Simple    squamous    cells.      ft.    Simple    cuboidal    cells. 


or  round  form.  They  occur  in  the  descending  limb  of 
Henle's  loop,  the  capsule  of  Bowman  in  the  kidney,  the 
alveoli  of  the  lungs,  and  in  parts  of  the  ventricles  of  the 
brain. 

b.     The  stratified  squamous  variety  consists  of  many 
layers  of  cells  that  are  unlike  in  form.     The  lowest  layer, 


Fig.  10. — Surface  View  of  Squam- 
ous  Cells   of   Frog^s   Skin. 


Fig.  11. — Squamous  Cell  Isolated. 


Fig.    12. — Stratified    Squamous 
Epithelium. 


the  germinal  stratum,  is  columnar,  while  those  cells  just 
above  are  polygonal.  The  succeeding  cells  become  more  and 
more  flattened,  forming  the  squames,  or  scales,  from  which 


EPITHELIAL    CELLS. 


43 


this  variety  receives  its  name.  It  is  found  covering  the  body 
as  the  epidermis,  Hning  the  mouth,  pharynx,  esophagus,  epi- 
glottis, vocal  cords  and  the  anus  and  vagina. 

2.     Columnar,     c.     Simple    columnar    cells    are    tall, 
cylindric  elements  arranged  in  a  single  layer.    The  nucleus  is 


<2^  /^  o 

Fig.  13. 
a.  Simple  Columnar  showing  Cuticular  Border,     h.  Simple  Ciliated  Cells, 
c.  Simple  Columnar  and  Goblet  Cells. 

usually  oval,  and  found  nearer  the  base  than  the  center  of 
the  cell.  The  variety  is  found  in  the  stomach  and  intestinal 
tract,  the  penile  portion  of  the  urethra  and  in  many  gland 
ducts.     Low  columnars  are  often  called  cuboidal. 

PsEUDOSTRATiFiED  cclls  are  simple  columnar,  or  ciliated, 
cells,  in  which  the  nuclei  are  not  all  basal,  but  occupy  differ- 


FiG.    14. 
a.   Isolated  Columnar  Cells,     h.   Isolated  Ciliated  Cells,     c.   Three  Stages 
of  Goblet  Cells. 


ent  levels,  thus  giving  the  appearance  of  several  layers  of 
cells,  where,  in  reality,  but  a  single  layer  exists. 

d.     Stratified  columnar  cells  consist  of  a  number  of 
layers  of  columnar  elements  superimposed  upon  one  another. 


44  THE   TISSUES. 

The  cells  are  not  as  large  as  the  preceding.  They  occur  in 
the  vas  deferens,  seminal  vesicles,  membranous  urethra  and 
the  ducts  of  some  glands. 

3.  Ciliated  cells,  e.  Simple  ciliated  cells  are  simple 
columnar  elements,  which  bear,  upon  their  exposed  surface, 
a  varying  number  of  hair-like  processes  called  cilia.  These 
possess  a  motion  that  is  directed  toward  the  outlet  of  the 
organ  in  which  these  cells  are  found.  They  line  the  oviducts, 
uterus,  smaller  bronchioles,  spinal  canal,  accessory  spaces  of 
the  nasal  fossae  and  the  ventricles  of  the  brain. 


Fig.  15. — Pseudostratified  Cells. 

f.  The  stratified  ciliated  cells  are  practically  stratified 
columnar  cells,  of  which  the  exposed  layer  alone  possesses 
cilia.  They  are  found  in  the  epididymis,  first  part  of  the  vas, 
middle  ear.  Eustachian  tube,  upper  part  of  the  pharynx,  in 
the  larynx,  trachea  and  nasal  tract. 

4.  Prickle  cells  are  polygonal  elements  that  possess  little 
spines,  which  project  from  the  sides  of  the  cells.  These, 
meeting  the  spines  of  other  cells,  prevent  the  cell-bodies  from 
touching.  In  this  way,  a  series  of  intercellular  bridges  and 
spaces  is  formed.  These  cells  are  found  in  the  epidermis, 
just  above  the  genetic  layer. 

5.  Goblet  cells  are  cells  of  the  cylindric  type,  distended 
with  a  peculiar  secretion  called  mucin.  When  filled,  they  re- 
semble a  goblet,  hence  the  name.  When  the  secretion  has 
been  discharged,  the  cells  are  long  and  slender,  the  part  con- 
taining the  nucleus  projecting  on  either  side.  Such  cells  are 
met  with  in  the  gastro-intestinal  and  respiratory  tracts. 


EPITHELIAL    CELLS. 


45 


6.  Transitional  cells  are  peculiar  stratified  elements  that 
are  neither  columnar  nor  squamous.  They  occupy  an  inter- 
mediate position,  as  all  the  cells  are  polygonal.  They  occur 
in  the  pelvis  of  the  kidney,  in  the  ureter,  bladder,  the  first 


Fig.    16. 

a.    Stratified   Columnar   Ceils.      &.    Stratif.ed   Ciliated   Cells,      c.    Stratified 
Columnar  Cells  showing  Goblet  Cells. 


portion  of  the  male  and  the  greater  portion  of  the  female 
urethra. 

7.     Pigmented  cells  are  polygonal  or  columnar  cells,  in 
which  the  protoplasm  contains  a  varying  number  of  pigment 


Fig.  17. — Transitional  Cells. 


granules.  The  former  shape  is  found  in  the  epidermis  of 
colored  races,  and  around  the  nipple  and  genitals  of  Cau- 
casians ;  the  latter  occurs  in  the  retina  of  the  eye,  and  the  pig- 
ment granules  obscure  the  various  parts  of  the  cell. 


46  THE   TISSUES. 

8.  Neuro-epithelial  cells  are  epithelial  cells  that  have  be- 
come so  differentiated  as  to  perform  a  nervous  function 
(special  sense).  They  differ  according  to  location,  and  will 
be  described  under  each  special  sense.  They  occur  in  the 
retina  (rods  and  cones),  in  the  internal  ear  (hair  and  pillar- 
cells),  in  the  olfactory  mucous  membrane  and  in  the  taste- 
buds. 

9.  Glandular  cells  also  vary  according  to  the  nature  of 
the  gland  in  which  they  are  found,  as  in  the  liver,  pancreas, 
etc. 

Mucous  membranes.  The  epithelial  surfaces  within  the 
body  are  termicd  Mucous  membranes.  Glands,  which  are 
evaginations  of  such  surfaces,  are  also  classed  with  mucous 
membranes.  Such  membranes  are  complexes  of  all  four 
varieties  of  tissues.  They  are  lined  by  epithelial  cells,  of 
any  of  the  varieties  above  mentioned,  that  rest  upon  a  deli- 
cate BASEMENT  MEMBRANE,  beneath  which  is  found  a  layer 
of  fibro-elastic  tissue  called  the  tunica  propria.  The  struct- 
ure is  limited,  peripherally,  by  a  layer  of  involuntary,  non- 
striated  muscle  tissue,  the  muscularis  mucosae.  The  latter 
is  not  always  present,  as  will  be  seen  when  the  various  organs 
are  studied  in  detail.  These  membranes  line  cavities  that 
communicate  normally  zvith  the  air  and  usually  secrele. 

As  some  writers  classify  Endothelial  cells  as  epithelial,  it 
is  well  to  consider  them  at  this  time,  so  as  to  contrast  them. 

Endothelial,  or,  better,  Mesothelial,  cells  are  thin,  flat- 
tened elements  possessing  a  large  projecting  nucleus.  They 
are  irregular  in  outline,  and  are  held  together  by  intercellu- 
lar cement.  They  never  occur  in  more  than  a  single  layer, 
and  form,  with  fibro-elastic  supportive  tissue,  the  subendo- 
thelial  connective  tissue,  a  Serous  Membrane.  A  Serous 
Membrane  possesses  neither  basement  membrane  nor  mus- 


MUCOUS  AND  SEROUS   MEMBRANES. 


47 


cularis  mucosae,  and  lines  cavities  that  do  not  communicate 
normally  with  the  air  and  never  secretes.  Such  membranes 
are  smooth,  moist,  glistening  and  transparent,  and  subject  to 
inflammations  different  from  those  of  the  foregoing. 
Openings  called  stomata  are  said  to  exist,  but  these  are 
now  considered  artifacts. 


B 


&       D 


Fig.  18. 

-Abdominal  Endothelium,  a.  Endothelial  cell :  h.  nucleus  of  cell ; 
c.  cell  boundary  ;  d.  stigmata  ;  e.  endothelial  cells  of  stomata ;  f.  sto- 
mata. B. — Mesenteric  Endothelium.  C. — Arterial  Endothelium. 
D. — Perivascular  Lymphatics,  a.  Endothelial  cells  of  lymphatics ; 
h.  bloodvessel    (arteriole). 


Serous  membranes  are  found  lining  joint-cavities,  the  cir- 
culatory and  lymphatic  systems  and  the  larger  serous  cavi- 
ties, the  pleural,  peritoneal  and  pericardial. 


48 


THE  TISSUES. 


CHARACTERISTICS. 

MUCOUS    MEMBRANES. 

SEROUS    MEMBRANES. 

Where  found 

Lining    cavities    that 

In  cavities  that  do  not 

communicate  normal- 

normally     communi- 

ly with  the  air. 

cate  with  the  air  (fe- 
male peritoneal  cav- 
ity  excepted). 

Lined  by 

Epithelial   cells    of   any 

Endothelial       (  M  e  s  o- 

variety. 

thelial)  Cells,  one 
layer. 

Secrete. . .  . 

With  few  exceptions. 
Epithelial     cells,    base- 

Do not 

Structure 

Endothelial    cells,    sub- 

ment    membrane,    tu- 

endothelial      connec- 

nica propria,    muscu- 

tive  tissue. 

laris  mucosae. 

Represents 

All    four    varieties    of 

But  three  varieties   (no 

tissue. 

muscular    tissue). 

A  description  of  epithelial  tissues  would  not  be  complete 
without  a  consideration  of  Glands.  A  Gland  is  an  evagina- 
tion  of  a  mucous  surface,  consists  of  epithelial  cells,  ar- 
ranged in  definite  groups,  and  performs  a  physiologic  func- 
tion.   These  groups  are  the  secretory  units  of  the  organ. 

As  these  units  are  of  different  shapes,  a  classification  of 
glands  is  necessary,  to  understand  and  separate  them. 

Tubular  Glands. 

Simple. 

Branched. 

Coiled. 

Compound. 
Tubulo-Alveolar  Glands. 
Alveolar,  or  Racemose  Glands. 

Simple. 

Compound. 


GLANDS. 


49 


Tubular.     Simple  tubular  glands   are   mere   cylindric 
depressions  in  the  mucous  membrane.    They  are  Hned,  usual- 


FiG.  19. — Gland  of  Lieberkuehn  from  a  Section  of  the  Large 
Intestine. 
a.  Lumen  ;  h.  secretion  of  cells ;  c.  nucleus  and  protoplasm  of  cell ;  d.  fun- 
dus  cells   at   the   beginning   of   secretion ;    e,   f.   goblet   cells  in   later 
stages;    g,    dying  goblet   cells    {Stdhr's   Histology). 


ly,  by  simple  columnar  cells.    They  occur  in  the  cardiac  end 
of  the  stomach,  and  in  the  small  and  large  intestines. 


50  THE  TISSUES. 

The  branched  tubular  are  like  the  above,  except  that  the 
lower  end  is  divided  into  two  or  more  secretory  units.  The 
lining  cells  may  be  columnar,  or  ciliated,  as  in  the  uterus. 
These  glands  are  found  in  the  fundus  and  pyloric  portion 
of  the  stomach,  in  the  duodenum  (Brunner's  glands),  in  the 
uterus,  and  in  the  prostate. 

Coiled  tubular  glands  are  really  simple  tubes,  the  secre- 
tory portion  of  which  has  become  coiled  and  convoluted  to 
occupy  as  small  a  space  as  possible.  The  lining  cells  are 
columnar  or  cuboidal  (low  columnar.)  Examples  are  the 
sweat  and  ceruminous  glands. 

Compound  tubular  glands  are  those  in  which  the  primi- 
tive tubules  have  divided  and  redivided  until  an  enormous 
number  of  divisions  has  resulted.  Pure  examples  of  this 
variety  are  the  liver  (also  called  reticular),  testicle,  kidney, 
thyroid,  lacrimal  and  serous  glands  of  the  mucous  mem- 
branes. 

Tubulo-alveolar  glands  are  those  in  which  the  terminal 
tubules  possess  sac-like  evaginations  along  the  walls.  Such 
glands  are  the  submaxillary,  sublingual,  prostate,  Brunner's, 
mammary  and  the  lungs. 

Alveolar.  The  simple  alveolar,  or  saccular,  glands  are 
sac-like  depressions  extending  from  the  free  surface.  They 
are  comparatively  few  in  number,  and  occur  as  the  smallest 
sebaceous  glands. 

The  COMPOUND  RACEMOSE  glauds  are  like  the  compound 
tubular,  except  that  the  terminal  portions  are  saccular,  in- 
stead of  tubular.  Such  glands  are  the  pancreas,  parotid, 
and  the  large  sebaceous  glands. 

As  a  rule,  all  glands,  at  some  period  in  their  development, 
are  connected  with  the  mucous  surface  by  a  tube  called  a 
duct.  This  connection,  in  most  instances,  persists,  but  where 
it  disappears,  the  gland  becomes  isolated,  and  the  term  duct- 


GLANDS 


St 


less  gland  is  applied.  Such  are  the  adrenals,  pituitary  and 
thyroid  bodies,  parathyroid,  carotid  and  coccygeal  glands, 
the  ovary  and  the  areas  of  Langerhans  in  the  pancreas.  These 
form  an  internal  secretion  that  is  absorbed  by  the  circulatory 
or  lymphatic  system. 


Fig.    20.-  Diagrams  op  Tubular 

Glands    (Stohr's  Histology). 
A.    Simple   tubular ;    B.    branched 

tubular  :    a.    excretory    duct ; 

C.   compound  tubular. 


Fig.    21. — Alveolo-Tubular 
Glands    (Stohr's   Histology). 
1.    Branched    alveolo-tubular ;    2. 
compound        alveolo-tubular ; 
a.   excretory   duct. 


The  function  of  a  gland  is  to  give  rise  to  a  substance  to  be 
used  by  the  body  in  some  of  its  many  processes.  This  sub- 
stance is  called  a  secretion,  and  it  may  be  liquid  or  cellular. 
(ovum).  The  liquid  secretions  may  be  serous,  mucous,  or 
mixed.     These  terms  apply  to  the  respective  glands  as  well. 

Serous  glands  are  those  which  form  a  thin  albuminous 


52  THE   TISSUES. 

secretion.     The  glandular  cells  respond  well  to  stains.     The 
parotid  and  pancreas  belong  to  this  class. 

Mucous  glands  are  those  that  give  rise  to  a  thick  viscid 
substance.  The  cells  here  stain  but  lightly  with  the  ordinary 
stains.  Such  are  the  small  glands  found  in  the  mouth, 
esophagus,  trachea  and  the  sublingual,  according  to  some 
writers.  ihhh  "^''W^ 


Fig.  22. — Alveolar  Glands    (Stohr's  Histology). 
1.   Alveolar  system  ;   2.   alveolar  compound  gland  ;   a.   excretory  duct. 

Mixed  glands  are  those  in  which  both  varieties  of  secre- 
tion are  formed.  The  secretory  areas  are  stained  darkly  or 
lightly,  according  to  whether  they  are  serous  or  mucous. 
The  sublingual  and  submaxillary  glands  are  examples,  and 
of  these,  the  latter  is  the  more  characteristic. 

The  minute  structure  of  glands  will  be  considered  under 
the  Alimentary  Tract. 

The  excretory  glands  are  the  kidneys,  lungs  and  sweat 
glands.  Each  will  be  considered  in  detail,  under  its  re- 
spective system. 


CHAPTER  IV. 


CONNECTIVE  TISSUES, 

The  Connective  Tissues  are  the  supportive  tissues  of 
the  body.  They  are  characterized  by  the  predominance  of 
the  inter celhdar  substance  over  the  cellular  elements.  This 
intercellular  substance  varies  in  the  different  forms,  as  will 
be  seen  when  each  is  considered. 

For  the  convenience  of  description,  this  class  has  been 
subdivided  into  the  following  varieties : 

Fibrous.  Modified. 


I. 

White. 

6. 

Adipose. 

a.     Loose. 

7. 

Adenoid. 

h.     Dense. 

8. 

Cartilage. 

2. 

Yellow  elastic. 

9- 

Bone. 

3. 

Mucous. 

10. 

Dentin. 

4- 

Retiform. 

II. 

Blood. 

5. 

Mixed. 

The  Fibrous  varieties  are  characterized  by  the  fibrous  or 
semi-solid  intercellular  substance.  The  cellular  elements 
are  comparatively  feziu,  and  are  found  scattered  among  the 
fibrils.  There  are  several  varieties  of  cells  found  in  con- 
nective tissues.  These  are  the  true,  or  fixed,  the  wandering 
and  the  plasma  cells.  The  true,  or  fixed,  connective  tis- 
sue cell  is  a  flattened,  stellate  element  with  many  processes 
that  extend  in  all  directions,  and  anastomose  with  those  of 
other  cells.  Within  the  network  thus  formed  lies  the  inter^ 
cellular  substance.  In  young  tissue,  the  cells  are  not  all  of 
the  above  form.  Some  are  round,  others  are  spindle-shaped ; 
these  gradually  become  converted  into  the  stellate  variety. 

The  WANDERING  Cell  passes  into  the  tissue  from  the  blood- 

53 


Fig.  23. 

-Mucous  Connective  Tissue,  a.  Spindle  cells  ;  h.  stellate  cell  ;  c.  inter- 
cellular substance.  B. — Cross  Section  of  Tendon,  a.  Epitendineum  ;  h. 
peritendineum  ;  c.  tendon  fasciculi  :  d.  interfascicular  space.  C. — 
Part  of  B,  highly  magnified,  a.  Epitendineum;  b.  cell  in  a;  c.  peri- 
tendineum ;  d.  tendon  fasciculus  ;  e.  interfascicular  space.  D. — Ten- 
don Cells  from  Interfascicular  Spaces.  E, — Elastic  Tissue  Cross- 
section  of  Ligamentum  Nuchae.  a.  Elastic  fibres ;  b.  white  fibrous 
supportive  tissue.  F. — E  highly  magnified,  a.  Elastic  fibres ;  b.  white 
fibrous  supportive  tissue.  G. — Areolar  Tissue,  a.  White  fibre  bundles  : 
b.  elastic  fibres ;  c.  spindle  cell  ;  d.  granule  cell  ;  e.  plasma  cell  ;  f. 
stellate   cell.     H. — Adipose  Tissue,     a.   Interlobular  connective  tissue  : 

b.  fat  cells ;  c.  nucleus  and  protoplasm  of  the  cell.  I. — H  highly 
magnified,  a.  Fat  cell  ;  b.  protoplasm  and  nucleus  of  cell.  K. — 
Lymphoid  Tissue,     a.  Leukocytes  ;   b.  stellate  connective  tissue  cells ; 

c.  reticulum.      L. — Pigmented   Connective  Tissue  Cell     trom   a   Pike. 


WHITE  FIBROUS  TISSUE  55 

vessels.  It  may  return,  or  remain  and  become  a  fixed,  or  true 
connective  tissue  cell. 

Plasma  cells  are  large  granular  fixed  elements,  especially 
noticeable  in  areolar  tissue.  They  are  at  first  oval  or  ob- 
long, and  later  change  to  the  stellate  type. 

The  INTERCELLULAR  substaucc  is  soft,  and,  in  most  varie- 
ties, fibrous.  These  fibrils  react  characteristically  to  certain 
stains,  as  will  be  pointed  out  later.  They  vary  in  thickness, 
and  are  arranged  in  bundles  which  may  be  parallel,  or  may 
interlace.  These  bundles  lie  in  a  more  or  less  homogenous 
ground  substance  that  varies  in  quantity  in  the  different 
varieties. 

The  origin  of  the  intercellular  substance  is  still  in  dispute. 
Two  theories  are  advanced.  According  to  some  writers,  it 
is  of  intracellular  origin,  while  others  claim  it  to  be  inter- 
cellular in  derivation;  in  other  words,  it  is  formed  in  the 
homogeneous,  semi-solid  intercellular  or  ground  substance, 
which  exists  before  the  fibrils  appear.  The  real  origin  is 
probably  by  a  combination  of  these  two  processes.  It  seems 
that  the  intercellular  substance  is  formed  from  the  peripheral 
protoplasm  of  the  cell,  which  becomes  fibrillar  in  character. 
This  small  amount  of  differentiated  protoplasm  is  then  sup- 
posed to  increase  itself,  and  so  give  rise  to  the  remainder 
of  the  fibrils. 

The  origin  of  the  elastic  fibres  is  not  so  plain,  both  of  the 
above  views  being  held  in  regard  to  them.  In  elastic  carti- 
lage, they  are  of  intercellular  origin,  but  still  the  intracellular 
formation  must  not  be  lost  sight  of. 

I.  White  fibrous  tissue  consists  of  fine  or  coarse 
bundles  of  inelastic  fibrils,  either  parallel  or  forming  a  deli- 
cate meshwork.  Its  two  subdivisions  are,  a,  loose,  and  b, 
dense. 

a.     Loose  fibrous  connective  tissue  is  a  minute  network 


56 


CONNECTIVE    TISSUES. 


of  small  bundles  of  fibrils  formed  for  the  support  of  capillary 
blood-vessels.  The  cellular  elements  are  of  the  types  named 
above,  and  are  few  in  number.  Upon  boiling,  it  yields  gela- 
tin, and  is  digested  by  pancreatin. 


Fig.  24. — Intermuscular  Connective  Tissue  Bundles  op  Man. 
a.  Fat  drop  ;  6.  fat  cells ;  c.  bundles  of  white  fibres ;  d.  nucleus  of  a  cell ; 
e.  elastic   fibres    {Stdhr's  Histology). 

It  forms  the  capsules  of  organs,  and  is  found  as  the  tunica 
propria  and  submucosa  of  the  alimentary  and  respiratory 
tracts. 

b.  In  the  dense  variety,  the  fibrils  are  coarser,  and  ar- 
ranged in  larger  bundles,  which  are  usually  parallel. 

Tendons  are  dense  white  fibrous  tissue,  in  which  all  the 
fibril  bundles  have  a  parallel  course.  The  whole  structure  is 
surrounded  by  a  sheath  of  looser  tissue,  called  the  epiten- 
dineum,  from  the  inner  surface  of  which  septa  are  sent  in 
that  divide  the  tendon  fibres  into  large  secondary  bundles. 


ELASTIC    AND    MUCOUS    TISSUES.  57 

These  latter  are  further  subdivided  into  primary  bundles, 
each  of  which  is  surrounded  by  a  minute  sheath,  the  peri- 
tendineum. Between  the  individual  bundles,  lie  the  peculiar 
tendon  cells.  These  are  flattened,  rectangular  elements  ar- 
ranged end  to  end  upon  the  tendon  bundles.  The  nuclei  are 
peculiarly  arranged.  In  two  adjoining  cells  they  will  be 
seen  near  the  line  of  junction,  but  in  the  cells  on  either  side 
of  these,  they  are  separated  by  nearly  the  length  of  the  two 
cells. 

In  FASCiA^,  the  bundles  are  large,  dense,  and  closely  packed. 

2.  Elastic  tissue,  as  its  name  indicates,  has  the  peculiar 
property  of  elasticity. 

The  fibres  are  yellow  in  color,  refractile,  and  coarser  than 
those  of  the  white  variety.  In  areolar  tissue,  they  are 
branched,  while  in  other  places  bands  and  even  membranes 
are  formed  (arteries).  When  separated  and  ruptured,  the 
torn  ends  curl.    This  occurs  in  no  other  tissue. 

This  variety  occurs  in  the  ligamentum  nuchae,  where  the 
fibres  are  very  heavy,  and  are  surrounded  by  white  inelastic 
fibres,  in  the  ligamentum  su'bflava,  in  blood-vessels,  and  in 
the  true  skin. 

Elastic  tissue  is  digested  by  pancreatin,  and,  upon  boiling, 
yields  elastin. 

3.  Mucous,  or  Embryonic,  connective  tissue  is  that 
variety  in  which  the  intercellular  substance  is  semi-fluid. 

The  cellular  elements  are  mostly  of  the  spindle-shaped 
variety,  although  numerous  stellate  cells  are  present.  Round 
cells  are  also  frequently  seen. 

The  intercellular  substance  is  semi-solid  in  the  youngest 
tissue,  and  takes  a  peculiar  homogeneous  stain.  As  the  tissue 
becomes  older  fibrils  begin  to  develop,  and  of  these,  the 
white  are  formed  into  bundles,  while  the  elastic  are  usually 
individual. 


S8  CONNECTIVE   TISSUES. 

Mucous  connective  tissue  is  found  in  the  umbilical  cord, 
in  embryos  and  in  the  vitreous  humor  of  the  eye. 

4.  Retiform  connective  tissues,  or  reticulum  is  the 
supportive  tissue  of  glands  and  gland-like  organs.  It  con- 
sists of  delicate  bundles  of  fibrils  forming  a  network,  in 
the  meshes  of  which  are  found  the  functionating  cells  of  the 
organ.  The  cells  are  chiefly  stellate  in  form,  and  their  pro- 
cesses anastomose  around  the  fibril  bundles. 

This  tissue  is  more  resistant  to  those  reagents  that  dissolve 
the  white  variety  (hydrochloric  acid  and  potassium  hydrate) 
and  yields  neither  elastin  nor  gelatin  upon  boiling,  nor 
is  it  digested  by  pancreatin. 

5.  MiXED_,  or  AREOLAR  Connective  tissue  is  a  combination 
of  the  white  and  elastic  varieties. 

The  white  tissue  is  present  in  the  form  of  delicate  bundles, 
and  these  form  a  loose  network  with  the  elastic  fibres,  which 
are  usually  thin  and  branched.  The  stellate  and  wandering 
cells  are  well  represented,  but  the  plasma  cells  are  more 
numerous  than  in  any  other  variety  of  tissue. 

This  variety  is  found  binding  the  skin  to  the  fascia  be- 
neath and  between  muscles. 

Modified.  In  these  varieties  of  connective  tissue,  the 
intercellular  substance  varies  from  liquid  (blood)  to  the 
hard,  unyielding  material  found  in  bone  and  dentin. 

The  cellular  elements  also  differ,  as  will  be  seen  when 
each  variety  is  discussed. 

6.  Adipose  tissue,  or  fat,  is  white  fibrous  tissue,  in  whirh 
the  cells  have  become  repositories  for  fat  globules.  These 
cells  are  quite  numerous,  but  the  stellate  shape  is  lost. 

The  minute  globules  unite  to  form  a  single  large  drop  that 
distends  the  delicate  cell-membrane.  By  this  coalescence, 
the  protoplasm  and  nucleus  of  the  cell  are  forced  to  one  side, 
and  are  seen  as  a  thin  hand,  or  crescent.  The  nucleus  may 
contain  vacuoles. 


LYMPHOID    TISSUE.  59 

Fat  cells  are  spherical,  when  not  closely  packed,  as  the 
fat  is  liquid  at  the  body  temperature.  After  death,  margarin 
crystals  are  seen  in  the  protoplasm.  The  cells  are  collected 
into  groups  called  lobules,  and  these  form  larger  masses 
called  lobes.  Blood-vessels,  nerve  and  lymphatics  are  present 
in  considerable  number.  The  first  named  are  especialh 
numerous,  as  there  is  a  close  relation  between  fat  deposition 
and  the  vascularity  of  the  part. 

According  to  some  writers,  fat  cells  are  specialized  con- 
nective cells  that  exist  in  no  other  form.  This  seems  doubt- 
ful, however,  as  experiments  have  shown  that  when  animals 
are  starved,  the  spherical,  fat-containing  cells  return  to  the 
stellate  form  as  the  fat  is  removed.  From  this,  it  would  seem 
that  these  cells  act  merely  as  storage  cells. 

When  adipose  tissue  is  studied,  after  ordinary  preparation, 
merely  a  network  of  fibres  and  cell  boundaries  is  seen.  This 
is  due  to  the  fact  that  the  fat  has  been  removed  by  the  alco- 
hol leaving  the  insoluble  white  fibrous  supportive  tissue.  In 
such  sections,  the  nucleated  crescents  of  protoplasm  are  read- 
ily observable.  In  sections  of  osmicated  fat,  the  peripheral 
cells  are  circular  in  outline,  while  the  deeper  ones  are  irregu- 
lar and  black,  due  to  the  action  of  the  osmic  acid,  which 
is  a  characteristic  reagent  for  fat.  Sitdan  III,  also  used  as 
a  test  for  fat,  stains  the  globules  dark  red. 

Adipose  tissue  is  found  widely  distributed  over  the  body, 
except  in  the  penis,  scrotum,  ear  and  eyelid.  From  the  orbit 
and  around  the  kidneys  it  never  entirely  disappears,  though 
death  be  due  to  starvation. 

7.  Adenoid,  or  lymphoid  tissue  is  a  special  form  of  the 
connective  variety  consisting  of  a  network  of  reticulum,  in 
the  meshes  of  which  are  found  lymphocytes,  or  zvhite  blood 
cells. 

These  cells  are  usually  the  small  lymphocytes,  although 


6o  CONNECTIVE   TISSUES. 

varying  numbers  of  the  large  lymphocytes  (hyalin  cells)  and 
poly  nuclear  cells  are  to  be  seen.  For  a  description  of  these 
cells,  see  blood  (p.  95). 

For  readiness  of  comprehension,  lymphoid  tissue  is  di- 
vided into  four  varieties:  a.  diffuse;  b.  solitary  follicle; 
c.  peyer's  patch,  or  agminated  follicle;  and  d.  lymph 

node,   or   GLAND. 

a.  Diffuse  adenoid  tissue  is  an  indefinite  collection  of 
leukocytes  in  an  organ.  The  cells  are  not  especially  arranged, 
neither  is  there  a  special  supportive  tissue  present,  as  in  the 
last  two  varieties. 

It  is  found  in  the  tunica  propria  of  the  alimentary  and 
respiratory  tracts,  and  the  cells  are  merely  scattered  be- 
tween the  bundles  of  white  fibrous  tissue.  It  forms  the 
medulla  of  the  thymus  body,  and  the  bulk  of  the  tonsil  and 
spleen,  and  is  transient  in  character. 

b.  Solitary  follicles  are  small,  dense  collections  of 
leukocytes  in  white  fibrous  tissue,  as  above.  There  is  no 
special  supportive  tissue  present;  although  the  outline  may 
be  slightly  irregular,  it  is  sharp.  Each  follicle  usually  shows 
a  lighter  center  in  which  the  cells  are  fewer  and  younger. 
This  is  called  the  germinal  center,  and  here  the  new  cells  are 
formed  by  karyokinetic  division. 

Solitary  follicles  are  found  in  the  alimentary  and  respira- 
tory tracts,  the  spleen  and  tonsil.  They,  like  the  diffuse 
variety,  are  transient  structures.     (See  Fig.  42,  page  103.) 

c.  A  PEYER^s  PATCH  is  a  morc  or  less  regular  collection 
of  solitary  follicles  sharply  outlined  from  the  surrounding 
tissue.  Each  patch  consists  of  ten  to  sixty  solitary  follicles, 
each  of  which  usually  shows  a  germinal  center.  (See  Fig. 
52,  p.  I2S). 

Peyer's  patches  are  found  in  the  ileum. 

d.  Lymph  nodes  (Lymph  Glands)  are  small,  bean- 
shaped  bodies  interposed  in  the  pathways  of  the  lymphatic 


CARTILAGE  6l 

vessels.  As  they  are  closely  related  to  the  Lymphatic 
System,  their  structure  will  be  there  considered. 

8.  The  CARTILAGES  are  characterized  by  a  solid  intercellu- 
lar substance.  The  cellular  elements  also  differ  from  those 
previously  described. 

Three  varieties  are  found  in  man:  the  hyalin,  white 
FiBRO  and  YELLOW  elastic. 

The  general  structure  will  first  be  considered,  under  peri- 
chondrhim,  cells  and  intercellular  substance. 

The  perichondrium  is  a  fibrous  sheath  that  surrounds 
cartilage  and  gives  rise  to  its  cellular  elements. 

It  is  composed  of  white  fibrous  tissue,  and  is  divided, 
functionally,  into  two  parts.  This  division  is  not  apparent 
under  the  microscope,  as  the  layers  fade  into  each  other. 
The  outer  part  is  the  fibrous  layer,  and  contains  few  cells. 
The  inner  portion,  or  chondro genetic  layer,  is  rich  in  cells 
that  are  not  of  the  stellate  type,  but  flattened  and  elongated, 
or  spindle-shaped.  These  are  the  chondroblasts,  which  be- 
come cartilage  cells.     Blood-vessels  also  are  present. 

The  cartilage  cells,  or  chrondroblasts,  vary  in  the  different 
portions  of  the  cartilage.  Just  beneath  the  perichondrium, 
they  are  flat  and  thin,  indicating  an  early  stage.  Toward  the 
center,  they  gradually  become  broader  until,  finally,  they 
are  oval  or  round  in  form.  Each  cell  is  rich  in  protoplasm, 
which  contains  one  or  more  vacuoles.  The  nucleus  is  usual- 
ly prominent.  The  cell  is  sharply  outlined  from  the  sur- 
rounding substance  by  a  thick  wall,  the  capsule.  This  is  a 
product  of  secretion  of  the  cell,  and  it  is  cast  off,  as  a  rule, 
every  time  the  cell  divides.  Each  cell  may  be  individual,  or 
several  may  be  seen  within  one  capsule,  which  is  due  to  the 
fact  that  the  new  cells  did  not  form  capsules  for  themselves. 
This  is  seen  especially  in  ossification  of  cartilage.  Between 
the  cell  and  the  capsule  is  usually  a  space  called  the  lacuna. 


62  CONNECTIVE    TISSUES. 

The  intercellular  substance  varies.  In  the  hyalin  variety, 
it  is  apparently  homogeneous ;  in  zirJiite  iihro,  it  is  composed 
mainly  of  white  fibrous  tissue,  while  in  the  yellow  Hhro  it 
consists  of  yellow  elastic  fibres. 

Hyalin  cartilage  is  a  peculiar  bluish  or  pearly  tissue, 
which  is  elastic,  and  readily  cut  with  a  knife. 

The  cellular  elements  are  as  above.  They  are  quite  numer- 
ous, and  close  just  beneath  the  perichondrium.  Further 
down,  a  number  are  usually  found  within  one  lacuna  and 
capsule. 

The  intercellular  substance  or  matrix,  is  apparently  homo- 
geneous. Upon  very  careful  study,  and  treatment  with  spe- 
cial reagents,  it  shows  a  fibrillar  character,  in  the  meshes  of 
which  is  seen  the  ground  substance,  which  is  homogeneous. 
This  ground  substance  is  formed  by  a  fusion  of  the  castoff 
capsules,  and  responds  very  well  to  hematoxylin,  showing 
a  peculiar  bluish  color. 

This  variety  of  cartilage  is  found  covering  articular  sur- 
faces, lining  joint-cavities,  as  the  costal,  tracheal  and  most 
of  the  laryngeal  cartilages.  It  precedes,  with  a  few  excep- 
tions, all  the  bones  of  the  body,  and  may  ossify  in  old  age. 

White  fibro  cartilage  consists  of  islands  of  the  hyaiir. 
variety,  separated  by  an  intercellular  substance  made  up  of 
delicate  bundles  of  white  Hbrous  tissue.  This  form  may 
ossify  or  calcify  in  old  age. 

It  is  not  very  abundant,  and  is  found  deepening  joint- 
cavities,  as  inter-articular  fibro-cartilages,  and  as  the  inter- 
vertebral discs. 

Yellow  fibro,  or  elastic  cartilage  is  that  variety  in 
which  the  intercellular  substance  is  composed  of  elastic 
fibres. 

It  is  practically  /lya/m  cartilage  in  which  the  hyalin  matrix 
has  been  replaced  by  elastic  tissue.     The  cartilage  cells  are 


CARTILAGE  63 

found  in  small  groups,  surrounded  by  only  a  small  amount 
of  the  hyalin  substance.  This  variety  never  ossifies  or  calci- 
fies, and  is  to  be  looked  for  in  regions  where  elasticity  is  re- 
quired, as  in  the  epiglottis,  ear.  Eustachian  tube  and  small 
laryngeal  cartilages. 


'  *       m     •'■* 


I 


r 


A  i3  C 

Fig.   25.-  Sections    of    Cartilage. 
— Hyalin   Cartilage,      a.    P^ibrous   layer   of   perichondrium ;    h.   genetic 
layer   of   pericliondrium ;    c.    youngest   chondroblasts ;    d.   older   chon- 
droblasts ;    e.   capsule  ;   f.   cells ;   g.    lacuna.      B. — Elastic  Cartilage. 
C. — White  Fibro-cartilage. 

Cartilage  contains  no  bloodvessels,  except  in  the  perichon- 
drium, and  during  the  developing  stage.  Lymph  channels 
are  said  to  be  absent,  so  that  its  nutrition  is  not  of  a  very 
high  order. 

9.  Bone  is  the  most  highly  differentiated  of  the  connect- 
ive tissues.     It  is  characterized  by  the  presence  of  a  very 


64  CONNECTIVE    TISSUES. 

hard,  unyielding  intercellular  substance  *that  has  a  character- 
istic arrangement. 

Bones,  like  cartilage,  are  surrounded  by  a  fibrous  sheath, 
the  periosteum,  beneath  which  is  the  hone  substance  proper ; 
the  latter  consists  of  cells  and  intercellular  substance. 

The  periosteum  is  composed  of  two  layers — outer,  or 
fibrous,  and  inner,  or  genetic. 

The  outer  layer  consists  of  white  fibrous  tissue,  support- 
ing a  large  number  of  bloodvessels,  and  containing  but  few 
cells.  The  inner,  or  genetic,  layer  is  rich  in  cells  and  capil- 
laries. These  cells  are  the  future  osteoblasts  that  secrete 
the  osseous  tissue.  From  its  inner  surface,  it  sends  in 
bundles  of  fibres  that  pierce  the  layers  of  bone  at  right 
angles,  and  bind  them  together.    These  are  Sharpey's  fibres. 

The  cells  are  all  of  the  irregular  stellate  type,  and  consist 
of  flattened  bodies  and  short  processes  that  extend  into  small 
canals,  to  be  described  later.  The  protoplasm  is  not  very 
abundant,  and  the  nuclei  are  oval,  and  often  vesicular. 

The  intercellular  substance  is  hard  and  resistant.  It  con- 
sists of  osseous  material  that  is  secreted  by  the  cells,  and  is 
peculiarly  arranged  in  the  compact  variety.  It  contains 
spaces,  or  lacunae,  from  which  extend  minute  canals,  or 
canaliculi.  Beside  these,  there  are  a  great  number  of  canals 
that  vary  in  length  and  diameter.  These  are  the  Haversian 
carnals. 

Bone  is  comiposed  of  inorganic  and  organic  salts;  the 
former  are  soluble  in  mineral  acids,  by  which  they 
may  be  removed  and  the  tissue  cut.  The  latter  are  removed 
by  burning ,  after  which  process  the  inorganic  substance  re- 
mains as  a  porous  mold  of  the  bone. 

There  are  two  varieties — cancellous,  or  spongy,  and 
COMPACT,  or  solid. 

Cancellous  bone  consists  of  spicules  forming  a  network 


BONE. 


65 


resembling  a  sponge.  These  spicules  have  a  fibrillar  struct- 
ure, and  contain  little  spaces,  called  lacunae.  In  the  living 
condition,  these  lacunae  are  occupied  by  bone-making  cells, 
termed  osteoblasts. 

This  variety  is  found  around  the  medullary  cavity  and  in 
the  heads  of  the  long  bones,  and  forming  the  central  portion 
of  the  flat  bones.  The  meshes  of  the  network  are  filled  with 
marrow. 


Fjg.   26. — Cross-section  of  Human   Compact  Bone. 
a.  Periosteum ;   Jj.   peripheral   lamellae :   c.   Ilaversian  canals ;  d.   lacunae ; 
6.     interstitial     lamellae ;     f.     perimedullary     lamellae ;     g.     marrow ; 
h.  Haversian  lamellae   {Stohr's  Histologi/). 


Compact  bone  has  a  characteristic  structure.  The  osse- 
ous matter  is  arranged  in  layers,  or  lamellae,  between  which 
lie  the  lacunae.  There  are  four  varieties  of  lamellae :  a.  Peri- 
osteal, peripheral,  or  circumferential;  b.  Haversian,  or  con- 
centric-; c.  Intermediate,  ground,  or  irregular ;  and  d.  Peri 
medullary,  or  Internal. 

a.  The  peripheral,  periosteal,  or  external  lamellae  arc 
those  formed  directly  from  the  periosteum.  They  are  few 
in  number,  and  several  are  required  to  complete  the  circum- 
ference.    Between  them  are  a  number  of  irregular  spaces, 


66  CONNECTIVE    TISSUES. 

lacunae,  from  which  Httle  canals  extend,  the  canaliculi.  The 
external  layer  has  a  number  of  small  depressions  called 
Howship's  foveae,  or  lacunae.  These  are  occupied  by  large 
bone  destroying  cells  called  osteoclasts.  Haversian  canals 
are  not  present,  but  larger  canals,  containing  blood-vessels 
from  the  periosteum,  are  seen.  These  are  Volkmanns 
canals. 

b.  The  Haversian  lamellae,  which  are  probably  the  most 
numerous,  are  thin  layers  circularly  arranged  around  a  small 
central  canal  called  the  Haversian  canal.  These  layers  are 
separated  by  the  lacunae,  and  pierced  by  the  canaliculi.  The 
lamellae  of  a  system  are  parallel  to  one  another,  but  the 
different  systems  usually  run  at  various  angles. 

An  Haversian  system  consists  of  the  lamellae,  canal, 
lacunae  and  canaliculi. 

The  canals  are  occupied  by  blood-vessels,  nerves  and 
lymphatics.  Those  nearest  the  marrow  cavity  contain  mar- 
row. The  canals  are  generally  parallel  to  the  long  axis  of 
the  bone,  and  anastomose  freely  with  one  another. 

c.  The  intermediate,  interstitial,  or  irregular  lamellae  lie 
between  the  Haversian  systems,  and  are  irregular  in  size  and 
form.  They  are  the  remains  of  Haversian  and  periosteal 
lamellae,  altered  by  the  growth  of  the  bone  in  diameter.  No 
canals  are  found  here,  but  lacunae  and  canaliculi  are  present 
between  the  lamellae. 

d.  The  perimedullary,  or  internal  lamellae  are  not  very 
regular,  and  are  found  surrounding  the  medullary,  or  mar- 
row cavity. 

The  lacunae  are  small,  irregular  spaces  found  between  the 
various  lamellae  throughout  the  bone,  and  occupy  a  portion 
of  each  of  the  adjacent  lamellae,  and  do  not  lie  in  one  alone. 
These  spaces  are  said  to  be  lined  by  a  delicate  membrane. 
They  contain  the  osteoblasts. 


BONE-MARROW.  67 

Extending  in  all  directions,  are  small  canals,  or  canaliculi. 
that  communicate  with  those  of  other  lacunae,  so  that  a  series 
of  intercommunicating  spaces  results.  Those  lacunae  lying 
nearest  the  Haversian  canals,  communicate  with  them,  but 
the  peripheral  ones  of  a  system  do  not  communicate,  to  any 
great  extent,  with  those  of  the  interstitial  lacunae.  The 
canaliculi  serve  as  supports  for  the  processes  of  the  osteo- 
blasts. 

The  MEDULLARY  CAVITY,  which  Contains  the  nutrient  mar- 
row, is  a  large  space,  in  the  shafts  of  the  long  bones. 

The  MARROW  is  of  two  varieties,  red  and  yellow.  The  red 
is  found  in  young  persons,  while  the  yellow  occurs  in  those 
above  the  prime  of  life.  The  difference  is  due  to  the  pres- 
ence of  a  great  deal  of  fat  in  the  yellow,  whereby  the  color 
becomes  changed. 

Marrow  consists  of  a  delicate  network  of  reticulum,  sup- 
porting a  close  capillary  plexus  and  a  number  of  different 
cells.  These  cells  are :  myelocytes,  or  marrow  cells  ;  nu- 
cleated RED  BLOOD  CELLS,  Or  ERYTHROBLASTS,  WHITE  BLOOD 
CELLS,  or  LEUKOCYTES,   and  MYELOPLAXES. 

Myelocytes  are  large  nucleated  masses  of  granular  proto- 
plasm. The  nucleus  is  usually  round,  and  the  granules  fine. 
The  latter  usually  react  to  the  acid  stain.  These  cells  may 
show  ameboid  movements,  and  are  found  in  the  blood  in 
certain  diseases. 

Erythroblasts,  or  nucleated  red  cells.  These  cells 
differ  from  the  ordinary  red  cells  in  possessing  a  nucleus, 
and  may  show  mitotic  figures.  They  vary  somewhat  in  size, 
but  are  seldom  over  9.5  microns  in  diameter.  By  a  loss  of  the 
nucleus,  these  cells  become  the  erythrocytes^  or  normal  red 
cells. 

The  LEUKOCYTES  are  usually  the  Unely  and  coarsely  granu- 
lar eosinophils,  and  the  basophils. 


H        The  I 


68  CONNECTIVE    TISSUES. 

Myeloplaxes,  or  osteoclasts,  are  very  large,  irregular 
cells.  The  protoplasm  is  abundant,  and  a  number  of  nuclei 
may  be  seen.  These  cells  are  of  great  importance  in  bone 
destruction,  from  which  the  term  osteoclast  is  derived.  They 
may  be  capable  of  ameboid  movements. 

Bones  are  nourished  by  blood-vessels  that  enter  through 
the  nutrient  foramen  and  pass  to  the  marrov^  cavity.  From 
here,  branches  are  sent  to  the  various  parts  by  way  of  the 
Haversian  canals.  Other  vessels,  derived  from  the  perios- 
teum, lie  in  Volkmann's  canals,  which  are  found  in  the  cir- 
cumferential lamellae. 

Nerves  and  lymphatics  accompany  the  blood-vessels. 

Development  of  Bone. — Bone  is  not  a  primary,  but  a 
secondary  tissue.  It  is  preceded  by  cartilage  or  by  fibrous 
tissue.  Bone  developed  from  hyalin  cartilage  is  called  en- 
dochondral, while  that  developed  in  fibrous  tissue  is  re- 
ferred to  as  INTRA-MEMBRANOUS  boUC. 

Endochondral  bone  formation  is  the  process  by  which 
the  hyalin  cartilage  is  converted  into  spongy  bone.  It  is,  in 
reality,  a  combined  process,  for  so  soon  as  the  spongy  bone 
is  formed,  this  is  changed  to  the  compact  variety  by  the 
intra-membranous,  or  periosteal  method. 

When  ossification  begins,  the  cartilage  cells  in  that  vi- 
cinity begin  to  multiply  rapidly,  and  arrange  themselves  in 
rows  parallel  with  the  long  axis  of  the  bone.  Multiplication 
is  most  rapid  in  the  center  of  the  area,  and,  as  a  result,  the 
new  cells  are  unable  to  form  new  capsules  for  themselves ; 
in  consquence,  a  large  number  are  seen  in  one  space  called  a 
primary  areola,  or  marrozv  space.  In  the  cartilage  between 
these  spaces,  calcareous  matter  is  deposited,  and  the  cells 
above  and  below  arrange  themselves  into  parallel  rows.  The 
cells  within  the  areolae  either  disappear,  become  osteoblasts, 
or  osteoclasts;  the  latter  dissolve  the  cartilaginous  and  cal- 


BONE  DEVELOPMENT.  69 

careous  partitions  between  the  spaces.  As  a  result  of  the 
latter,  larger  spaces  are  formed,  and  these  are  the 
secondary  areolae.  Those  cells  that  become  osteoblasts,  lay 
down  a  thin  layer  of  osseous  tissue  upon  the  remaining  par- 
titions, so  that,  at  first,  these  consist  of  a  core  of  calcific  ma- 
terial covered  by  a  thin  veneer  of  true  bone.  As  the  process 
continues,  the  calcareous  matter  is  entirely  removed,  and  is 
replaced  by  bone. 

While  these  changes  have  been  in  progress,  the  perichon- 
drium has  become  the  periosteum,  which  now  forms  osteo- 
blasts. These,  with  trabeculae  of  the  periosteum  and  blood- 
vessels, pass  inward  toward  the  center  of  ossification,  and 
enter  the  areolae.  This  vascularization  forms  the  first  mar- 
row. The  blood-vessels  pass  uprward  and  downward  from 
the  center,  following  the  process  of  calcification.  Gradu- 
ally, the  delicate  rod  of  cartilage  is  converted  into  a  rod  of 
spongy  bone.  The  articular  portions  are  separated  from 
the  shaft  by  an  interposed  disc,  the  epiphyseal  cartilage. 

Periosteal  bone  formation  now  begins.  The  inner  surface 
of  the  periosteum  becomes  converted  into  a  thin  layer  of 
osseous  tissue,  and  the  osteoblasts  remain  surrounded  by  a 
small  space  that  is  continued  along  its  processes.  This  space 
and  its  continuations  are  the  lacunae  and  canaliculi.  As  the 
inner  surface  is  changed  to  bone,  the  outer  surface  has  a 
corresponding  amount  added  to  it,  so  that  the  thickness  of 
the  periosteum  is  proportionately  the  same. 

With  the  formation  of  periosteal  bone,  the  various  lamellae 
are  formed.  The  peripheral  are  merely  the  converted  perios- 
teum. The  Haversian  systems  and  lamellae  are  formed  in 
the  following  manner.  From  the  inner  surface  of  the  peri- 
osteal layer,  projections  are  formed  at  various  angles.  These 
meet  other  projections,  thereby  enclosing  a  small  space,  the 
primitive  Haversian  canal.    Osteoclasts  gain  access  and  make 


70 


CONNECTIVE    TISSUES. 


this  Space  regular  and  larger.     Then  osteoblasts  lay  down 
layer  upon  layer  of  osseous  matter  until  only  a  small  channel, 


Fig.  27. — Cross-section  of  a  Developing  Bone  of  a  Human  Fetus  of 
Four  Months. 

o.  Periosteum ;  h.  boundary  between  endochondral  and  periosteal  bone ; 
c.  perichondral  bone ;  d.  remains  of  area  of  calcification ;  e.  endo- 
chondral bone;  f,  f.  blood-vessel;  g,  g'.  developing  Haversian  spaces; 
h.  marrow;  i.  blood-vessel   (Stohr's  Histology). 


the  Haversian  canal,  is  left.  The  remains  of  the  peripheral 
lamellae  between  the  various  systems  go  to  make  up  the 
interstitial  lamellae. 


BONE    DEVELOPMENT  71 

With  the  formation  of  the  peripheral  lamellae,  the  net- 
work of  spongy  bone  is  removed  from  the  center  by  osteo- 
clasis. This  leads  to  the  formation  of  a  marrow  cavity.  As 
the  bone  increases  in  size,  the  cavity  increases  in  proportion, 
by  the  destruction  of  the  surrounding  bone.  During  the 
prime  of  life,  hone  formation  exceeds  cavity  formation,  but 
in  old  age,  the  reverse  is  the  case,  sc  that  the  shaft  becomes 
thinner,  and  the  cavity  larger. 

The  bone  increases  in  diameter  by  the  continued  addition 
of  peripheral  lamellae,  as  a  tree  grows  in  thickness.  It  grozvs 
in  length  by  the  interposition  of  a  disc  of  cartilage  between 
the  shaft  and  head  of  the  bone.  In  this  disc,  new  cartilage 
is  formed  as  rapidly  as  ossification  occurs.  This  is  the  cam- 
bium  layer,  and  should  it  ossify,  that  end  of  the  bone  would 
no  longer  increase  in  length.  This  change  occurs  normally 
when  full  height  is  reached. 

This  method  of  bone  formation  occurs  in  all  bones  except 
those  of  the  face  and  of  the  vault  of  the  cranium. 

Intra-membranous  bone  formation  is  the  process  whereby 
white  fibrous  tissue  becomes  converted  into  bone.  Two  peri- 
osteal layers  are  present,  and  between  these,  the  bone  is 
formed.  Upon  the  fibrous  bundles  connecting  them,  osteo- 
blasts deposit  osseous  material  until  all  are  converted  at 
the  same  time  the  formation  of  Haversian  systems  occurs. 

Such  bones  increase,  in  thickness,  as  above,  and  laterally, 
by  the  maintenance  of  a  layer  of  fibrous  tissue  at  its  edges. 
This  is  the  cambium  layer,  and  when  full  growth  is  attained, 
this  layer  ossifies,  and  union  occurs  between  the  various 
bones. 

ID.     Dentin  will  be  considered  under  the  teeth. 

II.  Blood  is  the  only  liquid  connective  tissue.  As  it  is 
part  of  the  circulatory  system,  it  will  be  considered  when 
that  is  described. 


CHAPTER  V. 


MUSCULAR  TISSUES. 

Muscular  tissues  are  those  which  produce  the  various 
movements  of  the  body,  whether  voluntary  or  involuntary. 

Like  epithelial  tissues,  they  consist  chiefly  of  cellular  ele- 
ments, the  intercellular  substance  being  small  in  amount. 
The  varieties  are  voluntary  striated,  involuntary  non- 
striated  and  involuntary  striated.  Voluntary  striated 
muscles  are  characterized  by  being  under  the  control  of  the 
will. 

Each  MUSCLE  consists  of  a  large  number  of  tmits  called 
fibres,  bound  together  by  white  fibrous  tissue. 

Each  fibre,  or  cell,  is  a  narrow  cylinder.  It  varies  from 
one  to  ^\t  inches  in  length,  and  exhibits  cross  and  longitudi- 
nal  striations.  It  is  composed  of  a  large  number  of  fibrillae, 
which  are  surrounded  by  a  membrane  called  the  sarcolemma, 
and  separated  from  one  another  by  sarcoplasm.  Many  peri- 
pherally located  nuclei  are  present. 

The  fibrillae  consist  of  sarcous  elements  which  stain  darkly 
and  are  doubly  refractile,  or  anisotropic.  The  sarcoplasm 
is  a  palely  staining,  semi-solid  substance  that  lies  between 
the  fibrillae,  and  is  singly  refractile,  or  isotropic. 

The  longitudinal  striations  are  formed  by  the  alteration  of 
the  fibrillae  and  the  sarcoplasm,  and  are  usually  not  as  dis- 
tinct as  the  cross,  though  at  times  the  reverse  is  the  case. 
The  cross  striations  .are  due  to  the  alternation  of  light  and 
dark  discs,  or  bands.  The  dark  bands,  or  Brueckers  lines, 
are  composed  of  rows  of  parallel  sarcous  elements,  separ- 
ated by  the  sarcoplasm.  These  sarcous  elements  are  cylin- 
drical, except  at  the  ends,  where  they  are  cone-shaped.  The 
ends  form  part  of  the  light  disc.  Each  dim  band  is  divided 
transversely  by  a  less  refractile  line,  called  Hensen's  disc. 

72 


VOLUNTARY   MUSCLE.  73 

The  light  discs  are  subdivided  into  three  portions,  an 
intcrmediaie  and  tzi^o  lateral.  The  intermediate  disc  con- 
sists of  a  single  row  of  small  globules,  interposed  between 
the  apices  of  the  cones.  These  are  Dobie's  globules,  or  the 
membrane  of  Kranse.  The  lateral  discs  are  merely  the  cone- 
shaped  continuations  of  the  sarcous  elements.  They  are-  a 
little  dimmer  than  the  intermediate  disc.  It  will  be  seen  from 
the  figure  that  the  main  portion  of  this  light  disc  consists  of 
the  refractile  sarcoplasm. 

The  nuclei  are  numerous,  and  are  found  beneath  the  sar- 
colemma,  but  external  to  the  muscle  substance.  They  are 
long  and  rather  narrow,  but  respond  well  to  the  stain. 

The  SARCOLEMMA  is  a  delicate  fibrous  sheath  that  lies 
close  to  the  fibre.  It  is  not  seen,  as  a  rule,  except  by  special 
preparation.  If  a  fresh  muscle  fibre  be  treated  with  water, 
the  muscle  substance  ruptures,  and  the  delicate  membrane  is 
shown  spanning  the  interval. 

Upon  cross-section,  the  fibres  show  a  sharp  outline,  and 
the  peripheral  nuclei  are  readily  distinguished.  Upon  care- 
ful observation,  the  fibrillae  are  seen  collected  into  groupS; 
constituting  Cohnheim's  fields. 

Contractility  is  an  inherent  quality  of  the  sarcous  ele- 
ments, but  the  sarcoplasm  does  not  possess  it.  Occasionally, 
among  the  tongue  muscles  are  found  some  fibres  that  branch. 
Such  fibres  are  numerous  in  the  tongue  of  the  frog. 

Muscles.— Fibres  are  collected  into  definite  groups  called 
Muscles.  Each  muscle  is  surrounded  by  a  sheath  of  white 
fibrous  tissue  called  the  epimysium.  From  its  inner  surface, 
septa  are  sent  in  that  divide  the  muscle  into  a  number  of 
large  secondary  bundles.  These  secondary  bundles  are 
further  subdivided  into  primary  bundles^  or  fascicvdi,  which 
are  invested  by  a  sheath,  the  perimysium.  This  sends  in 
fibres  that  pass  between  the  individual  fibres,  and  these  rep- 


74 


MUSCULAR   TISSUES. 


^Si^^'    ,'«■  -\      ">'v 


^7 ♦ 

a— 


r 


'^fp 


■■-A 


^^■^^ 


Fig.  28. 

A. — Longitudinal  section  of  smootli  muscle  fibres — a.  muscle  fibre ;  6.  nu- 
cleus ;  c.  fibrous  tissue  between  fibres.  B. — Cross-section  of  smooth 
muscle  fibres — a.  perimysial  connective  tissue  ;  h.  blood-vessel ;  c.  nu- 
cleated fibre  ;  d.  nonnucleated  fibre.  C. — Longitudinal  section  of  vol- 
untary muscle  fibres. — a.  sarcolemma  ;  b.  nucleus  ;  <?.  end  of  muscle 
fibre  ;  d.  dark  bands  ;  e.  intermediate  disc ;  f.  nucleus  ;  g.  lateral  discs. 
D. — Diagrammatic  section  of  cross  and  long  striations — a.  dark  disc  ; 
h.  lateral  discs  ;  c.  intermediate  disc.  E. — Cross  section  of  voluntary 
muscle — a.  perimysium  ;  h.  endomysium  ;  c.  nucleus  of  perimysium  ;  d. 
fibrillae  :  e.  nucleus  of  muscle  ;  /.  sarcolemma.  F. — Longitudinal  sec- 
ton  of  cardiac  muscle  fibres — a.  muscle  fibre  ;  h.  nucleus  ;  c.  branch. 
G. — Cross  section  of  cardiac  muscle  fibres — a.  perimysial  sheath  ;  6. 
nucleus  of  sheath  ;  c.  muscle  fibre ;  d.  nucleus ;  e.  radial  plates  of 
fibrillae. 


SMOOTH    MUSCLE  75 

resent  the  endomysium.  Where  the  muscle  joins  the  tendon, 
the  nuclei  are  especially  numerous. 

The  blood-vessels  pierce  the  epimysium  and  form  branches 
that  follow  the  larger  septa  and  ultimately  reach  the  perimy- 
sium, where  smaller  branches  are  formed.  These  pierce  the 
perimysium,  and  form  longitudinal  capillary  meshes,  which 
anastomose  and  at  intervals  show  peculiar  dilatations. 

Lymphatics  are  usually  not  numerous,  and  may  even  be 
wanting. 

The  nerves  follow  the  bloodvessels,  but  the  exact  method 
of -termination  will  be  considered  under  Nerve  Endings. 

Voluntary  striated  muscles  are  found  as  the  skeletal  and 
external  ocular  muscles,  in  the  tongue,  pharynx,  upper  part 
of  the  esophagus,  anus,  diaphragm,  and  in  the  external  ear 
and  larynx. 

The  Involuntary  Nonstriated,  or  Smooth,  muscle  is  not 
under  the  control  of  the  will. 

The  individual  fibres  are  short,  narrow  and  spindle- 
shaped.  Each  is  usually  25  p-  to  200  p-  in  length,  and  5  to  70 
microns  in  breadth. 

No  sarcolemma  is  present,  and  striations  are  absent. 

In  each  fibre  there  is  but  one  niicleiis,  which  is  long, 
slender,  darkly  staining  and  centrally  located.  This  is  not 
seen  in  all  cross-sections,  but  when  present,  shows  as  a 
small,  dark  dot. 

These  fibres  vary  in  length  from  25  to  200  microns,  ordi- 
narily, but  in  the  gravid  uterus  may  attain  a  length  of  600 
microns.     In  diameter,  they  average  about  5  microns. 

The  fibres  are  arranged  in  bundles  like  the  above,  but  in- 
stead of  forming  masses  like  muscles,  the  bundles  are  ar- 
ranged into  layers,  which  extend  circularly  and  longitudinal- 
ly, in  the  hollow  viscera. 

Capillaries  exist  between  the  fibres  as  above. 


76  MUSCULAR   TISSUES. 

The  nerves  are  chiefly  of  the  sympathetic  variety. 

Invohintary  muscles  are  found  in  the  ahmentary  tract 
from  the  middle  third  of  the  esophagus  to  the  anus,  in  the 
ducts  of  glands,  in  the  trachea  and  bronchial  tubes,  within 
the  eyeball,  the  internal  urinary  and  genital  systems,  circu- 
latory (except  the  heart)  and  lymphatic  systems,  and  the 
capsules  of  some  organs. 

Involuntary  Striated,  Cardiac,  or  Branched  Muscle 
is  that  variety  found  in  the  heart. 

The  fibres  are  short,  stubby  cylinders,  possessing  stria- 
tions  but  no  sarcolemma,  although  a  delicate  investing  sheath 
is  present.  These  fibres  vary  from  100  to  200  microns  in 
length,  and  25  to  40  microns  in  breadth. 

A  single  large,  oval,  centrally  placed  nucleus  is  also  pres- 
ent ;  this  is  usually  surrounded  by  a  peculiar  zone  of  proto- 
plasm, in  which  pigment  granules  may  be  found.  Some- 
times there  are  two  nuclei. 

The  transverse  striations  are  usually  fainter  than  the  longi  - 
tudinal. 

A  peculiarity  of  this  variety  is  that  the  fibres  branch. 
These  branches  are  short  and  narrower  than  the  cell-body, 
and  anastomose  with  the  branches  of  other  cells. 

In  cross-sections,  the  fibrillae  are  seen  to  be  particularly 
arranged.  They  are  formed  into  radial  plates  that  start  from 
the  center  or  the  zone  of  undifferentiated  protoplasm  that 
surrounds  the  nucleus. 

The  blood-vessels  enter  into  intimate  relation  with  the 
fibres,  and  are  derived  from  the  coronary  arteries,  the 
smaller  branches  of  which  lie  between  the  muscle  bundles. 
The  capillaries  pass  into  these  and  run  parallel  to  the  fibres, 
in  which  they  often  lie  in  grooves,  and  are  frequently  seen 
within  the  fibre,  surrounded  by  the  muscle  substance. 


CARDIAC    MUSCLE 


n 


The  nerves  are  both  sympathelic  and  eerebro-spinal.  Sym- 
pathetic  ganglia  are  also  present. 

The  following  table  will  give  the  various  characteristics 
of  the  muscular  tissues  in  comparison. 


CHARACTERISTIC. 

VOLUNTARY  STRIATED. 

SMOOTH. 

CARDIAC. 

Shape. 

Long  cylinder. 

Spindle. 

Stubby  cylinder. 

Nucleus. 

Number. 

Many. 

One. 

One. 

Location. 

Peripheral. 

Central. 

Central. 

Shape. 

Intermediate. 

Rod. 

Oval. 

Striations. 

Cross  and  long. 

None. 

Cross  and  long. 

Sarcolemma. 

Present. 

None. 

None. 

Branches. 

Occasional. 

None. 

Always. 

CHAPTER  VI. 


NERVOUS  TISSUES. 

The  Nervous  Tissues  are  the  most  highly  differentiated 
of  all  the  tissues. 

There  are  two  varieties,  gray  and  white.  The  gray  is 
characterized  by  a  grayish  color,  and,  in  the  central  nervous 
system,  is  divid-ed  into  layers.  In  the  spinal  cord  and 
ganglia,  its  arrangement  is  different.  It  consists  of  cells 
and  INTERCELLULAR  SUBSTANCE,  the  latter  of  which  is  called 

the   NEUROGLIA,   Or   SUPPORTIVE   SUBSTANCE. 

A  typic  nerve  cell  consists  of  a  cell-body,  from  which  a. 
number  of  processes  extend,  a  nncleus  and  nucleolus.  The 
whole  structure  is  also  called  a  neuron. 

The  cell-body  consists  of  granular  and  fibrillar  proto- 
plasm, which  at  the  point  of  origin  of  the  main  process  is 
formed  into  a  mass,  the  axis  cylinder  hillock.  Besides  the 
usual  granules  some  very  large  darkly  staining  bodies  are 
seen  in  the  vicinity  of  the  nucleus.  These  are  the  corpuscles 
of  Nissl,  or  the  tigroid  bodies.  The  nucleus  is  usually  large 
and  vesicular  while  the  nucleolus,  also  large,  stains  very 
darkly  and  is  quite  prominent. 

The  processes  are  of  two  varieties,  axis  cylinder  and  den- 
dritic. The  axis  cylinder,  or  neurit,  is  the  main  and  largest 
process.  It  forms  the  means  of  communication  between  the 
cells  of  an  area  or  those  in  different  regions.  It  arises  at  the 
hillock  and  consists  of  fibrillated  protoplasm.  The  dendrites 
are  usually  shorter,  and  branch  a  great  deal.  They,  ap- 
parently, also  afford  communication  between  the  cells  of  a 
region. 

There  are  three  varieties  of  cells  according  to  the  number 
of  processes :  unipolar,  bipolar  and  multipolar. 

78 


NERVE   CELLS.  79 

The  UNIPOLAR  CELLS  are  those  possessing  but  one  process, 
In  the  early  embryonal  condition  two  were  in  reality  present 
but  the  growth  of  the  cell  was  such  that  the  two  were  thrown 
together  as  one.  The  individuality  of  each  portion,  how- 
ever, is  retained.     These  cells  occur  in  the  spinal  ganglia. 

The  BIPOLAR  CELLS  are  those  having  two  processes.  The 
dendritic  process  very  rapidly  breaks  up  into  a  great  num- 
ber of  smaller  ones  called  telodendrites.  This  variety  is 
found  in  the  cerebellum.   i{j^^iyy^ 

The  MULTIPOLAR  CELLS  which  are  the  most  numerous, 
have  three,  or  more,  processes.  They  are  found  in  the  cere- 
brum, cerebellum  and  spinal  cord. 

There  are  two  types  of  cells  according  to  the  course  of 
the  axis  cylinder.  In  cells  of  the  first  type  (Deiter's 
cells)  the  axis  cylinder  leaves  the  gray  matter  to  become 
a  nerve  Hbre.  In  the  second  type  (Golgi's  cells)  the  axis 
cylinder  never  leaves  the  gray  matter. 

The  neuroglia  is  the  distinctive  supportive  structure  of 
the  nervous  system.  It  is  not  connective  tissue.  Unlike  the 
intercellular  substances  elsewhere  it  is  not  the  result  of  the 
secretion  of  the  functionating  cells  (nerve  cells)  but  is 
formed  by  special  cells  called  neiiroglia,  or  glia  cells.  These 
cells  secrete  the  intercellular  substance  of  the  neuroglia. 

The  glia  cells  are  of  two  varieties,  spider  and  mossy. 

The  spider  cells  possess  small  bodies  which  send  out  many 
thick  branches  varying  in  length.  They  are  found  in  the 
white  matter  and  their  processes  interlace  to  form  a  suppor- 
tive network  for  the  nerve  fibres.  They  are  the  more 
numerous. 

Mossy  cells  possess  larger  cell-bodies  but  shorter  pro- 
cesses that  are  finer  and  more  branched.  They  occur  chiefly 
in  the  gray  matter. 

In  addition  to  the  above  a  small  amount  of  connective 


V 


8o  NERVOUS  TISSUES. 

tissue  is  found  in  the  grey  matter.  This  penetrates  with  the 
blood-vessels. 

The  gray  matter  is  found  in  the  cerebrum,  cerebellum, 
pons,  medulla,  spinal  cord  and  ganglia. 

The  White  matter  consists  of  medullated  nerve  fibres 
bound  together  by  neuroglia  and  connective  tissue,  the  latter 
of  which  supports  the  blood-vessels  chiefly. 

Nerve  Fibres,  the  continuations  of  cells  of  the  first  type, 
are  of  two  varieties,  Medullated  and  Nonmedullated. 

Medullated  nerve  fibres  have  a  characteristic  structure. 
Each  consists  of  an  axis  cylinder  that  lies  in  the  center 
and  represents  the  cell  and  shows  a  fibrillated  structure 
somewhat  like  that  of  a  muscle  fibre.  This  axis  cylinder  is 
surrounded  by  a  delicate  membrane,  the  asilemma. 

The      MEDULLARY      SHEATH,      Or      WHITE      SUBSTANCE      OF 

Schwann,  surrounds  the  axis  cylinder.  It  consists  of  a  fine 
network  of  kerato-hyalin  containing  in  its  meshes  a.  fatty 
substance,  the  myelm.    The  latter  is  blackened  by  osmic  acid. 

The  NEURILEMMA,  or  SHEATH  OF  ScHWANN  is  a  tender 
covering  that  enfolds  the  individual  nerve  fibre. 

At  regular  intervals  are  annular  constrictions,  where  the 
neurilemma  dips  and  touches  the  axis  cylinder.  These  places 
are  the  nodes  of  Ranvier,  and  at  such  points  the  axis  cylin- 
der may  give  off  branches  called  collaterals.  The  portion 
between  the  nodes  is  an  internode;  each  contains  a  nucleus. 
In  the  internodes,  funnel-shaped  depressions,  the  clefts  of 
Lantermann,  are  seen. 

A  Nonmedullated  nerve  fibre  is  one  that  possesses  no 
medullary  sheath.  It  is  merely  a  naked  axis  cylinder  sur- 
rounded by  its  axilemma.  All  the  sympathetic  fibre  are  of 
this  variety  but  some  are  found  in  the  cerebro-spinal 
system. 


NERVE  CELLS  AND  FIBRES. 


8i 


e~m 


Fig.  29. 
Multipolar  cell  from  cerebral "  cortex ;  B.  multipolar  cell  from  spinal 
cord  ;  C.  pyramidal  cell  from  cerebral  cortex  ;  D.  unipolar  cell  :  E.  bi- 
polar cell  ;  F.  cell  of  Purkinje,  antler  cell  :  G.  mossy  cell  ;  H.  spider 
cell  :  I.  cell  from  spinal  cord  of  an  ox,  showing  pigment  granules ; 
K.  ganglion  ;  L.  sympathetic  or  nonmedullated  fibres  ;  M,  longitudinal 
section  of  medullated  nerve  fibre — a.  neurilemma :  h.  medullary 
sheath  ;  c.  axis  cylinder ;  d.  node  of  Ranvier :  e.  nucleus ;  N.  cross- 
section  of  osmicated  nerve  fibres :  O.  medullated  nerve  fibre  of  a 
guinea-pig  showing  the  reticulum  ;  P.  medullated  nerve  fibres  of  a 
toad,  showing  reticulum  (kerato-hyalin)  ;  K.  motor  neuron,  showing 
nerve  cell,  dendrites,  axis  cylinder  and  ending  of  latter  in  a  muscle ; 
S.   cross-section  of  nerve  trunk. 

S 


/ 


82  NERVOUS  TISSUES. 

A  Nerve  is  a  collection  of  nerve  fibres  arranged  in  a  defi- 
nite manner. 

Each  Nerve  is  surrounded  by  a  sheath  of  w^hite  fibrous  tis- 
sue, the  EPiNEURiUM.  From  this,  septa  pass  inward  and  di- 
vide the  nerve  into  large  secondary  bundles  that  are  further 
subdivided  into  primary  bundles,  or  fasciculi,  each  of  v^hich 
is  surrounded  by  the  perineurium.  The  fibres  contained 
in  the  fasciculi  are  separated  from  one  another  by  the 
endoneurium,  which  is  a  continuation  of  the  perineurium. 

The  blood-vessels  pierce  the  epineurium  and  branches  are 
sent  along  the  septa  into  the  primary  bundles.     Here  capil 
laries  are  formed,  which  run  parallel  to  the  fibres.     These 
vessels  are  the  vasa  nervorum. 

Ganglia  are  collections  of  gray  matter  and  are  found  in 
the  cerebrum,  as  the  basal  ganglia;  in  the  sympathetic  sys- 
tem, as  the  sympathetic  ganglia;  and,  just  outside  of  the 
vertebral  canals,  as  the  spinal  ganglia. 

A  Ganglion  consists  of  a  limiting  sheath,  or  capsule  of 
white  fibrous  tissue  within  which  the  nerve,  or  ganglion 
cells  are  found. 

The  ganglion  cell  is  a  large  spherical  element. surrounded 
by  a  distinct  space  (lymph  space)  lined  by  endothelial  cells, 
and  consists  of  granular  protoplasm  containing  a  large, 
palely  staining  nucleus,  and  a  distinct  nucleolus.  It  is  usually 
of  the  unipolar  variety.  Between  these  cells  are  seen  medul- 
lated  and  nonmedullated  nerve  fibres,  and  connective  tissue 
containing  blood-vessels  and  lymphatics. 

Nerve  Endings.  Nerves  terminate  in  Sensory  and 
Motor  endings. 

The  Sensory  endings  are  free,  tactile  cells  and  cor- 
puscles. 

Free  endings  are  found  in  mucous  membranes,  especially 
in  stratified  epithelium.    The  nerve  fibres  reach  the  basement 


TACTILE  CORPUSCLES. 


83 


membrane  and  upon  piercing  this  lose  their  neurilemma  and 
medullary  sheath.  These  branches  then  divide  repeatedly 
between  the  epithelial  cells. 

Tactile  cells  are  simple  and  compound. 

The  simple  variety  consists  of  a  disc-like  structure,  6  to  12 
microns  in  size,  which  lies  within  the  epithelial  layer.  To 
this  disc  passes  a  naked  axis  cylinder  and  upon  the  disc  lies 
the  tactile  cell  which  is  a  mass  of  granular  protoplasm. 

Compound  tactile  cells  consist  of  two  or  more  discs  con- 
taining between  them  the  tactile  cells.    A  branch  of  a  medul- 


"X        J 

Fig.  30. — Vertical  Section  of  Skin  of  Great  Toe  of  a  Man. 

A.  Epidermis ;  B.  derma;  a.  tactile  cell;  h.  tactile  meniscus;  c.  nerve 
fibre  ;  d.  connective  tissue  sheatli  of  same  ;  x.  tactile  cells  in  derma. 
{Stdhr's  Histology.) 


lated  nerve  fibre  passes  to  each  cell.  These  structures  arc 
usually  15  by  30  microns  in  size. 

Tactile  Corpuscles,  or  End-bulbs  are  the  most  differenti- 
ated of  these  endings.  They  vary  in  complexity  from  the 
comparatively  simple  genital  and  conjunctival  cor- 
puscles to  the  corpuscles  of  Meissner  and  Vater. 

The  genital  and  conjunctival  corpuscles  are  spherical 
bodies  in  which  the  cells  are  not  regularly  arranged.  The 
nerve  fibres  end  probably  between  the  cells. 

The  CORPUSCLE  of  Meissner  is  a  complex  structure  in 
which  the  individual  cells  cannot  be  distinctly  seen.     It  is 


84  NERVOUS  TISSUES. 

surrounded  by  a  sheath  that  encloses  a  number  of  trans- 
versely placed  nuclei.  One  or  more  nerve  fibres  pass  to  each 
corpuscle  and  upon  entrance  the  neurilemma  is  lost.  The 
medullary  sheath  soon  follows  and  the  axis  cylinders,  after 
a  spiral  course  are  thought  to  terminate  in  the  end  discs. 
These  bodies  measure  35  to  50  microns  by  45  to  100  and  are 
found  in  the  palmar  and  plantar  surfaces  of  the  true  skin. 

Corpuscles  of  Vater,  or  Pacinian  bodies  have  a  very 
definite  structure.     Each  consists  of  a  capsule,  inner  bulb 


Fig.  81. — Corpuscle  of  Meissner  from  Great  Toe  of  Man. 
n.    Medullated   nerve    fibre ;    h.    connective   tissue    sheath ;    e.   varicosities, 
'j-he  nuclei  are  invisible.      {Stohr's  Histology.) 

and  end-knob.  The  capsule  consists  of  lamellae,  of  con- 
nective tissue  concentrically  arranged,  which  are  usuallv 
bound  together  by  an  intracapsular  ligament.  The  layers 
are  covered  by  endothelial  cells  and  represent  so  many  lymph 
spaces. 

The  inner  bulb  is  an  elongated  cylindric  mass  of  granu- 
lar protoplasm  that  receives  the  axis  cylinder  of  the  nerve. 
-  As  the  nerve  pierces  the^  capsule  the  neurilemma  is  lost. 
When  it  reaches  the  inner  bulb  the  medullary  sheath  disap- 
pears and  the  naked  axis  cylinder  continues  through  the  inner 
bulb  and  ends  in  a  club-like  mass,  the  end-knob. 


MOTOR  ENDINGS 


85 


These  corpuscles  occur  in  the  derma,  near  joints,  in  the 
mesentery  (especially  in  lower  animals)  and  along  tendons. 

The  Motor  endings  of  the  voluntary  muscles  are  chiefly 
from  medullated  fibres.  After  piercing  the  epimysium,  the 
nerve  follows  the  septa  to  the  primary  bundles  and  breaks  up 
into  fibres  of  which  each  muscle  fibre  receives  one.  The 
neurilemma  and  medullary  sheath  of  the  nerve  fibres,  upon 
passing  through  the  sarcolemma  blend  with  it,  and  the  axis 


Fig.   32. — Pacinian  Body  from  Mesentery  of  a  Cat. 

1.  Fat   cells ;   2.   artery ;   3.   nerve  fibre :   4.   inner   bulb ;   5.   axis-cylinder ; 
6.  layers  of  the  capsule   {Stohr's  Histology). 


cylinder  breaks  into  fibrillae  each  of  which  forms  a  number 
of  bulbous  enlargements  that  pass  to  a  sole-plate.  This  sole- 
plate  consists  of  a  mass  of  nucleated,  granular  protoplasm 
and  with  the  bulbous  nerve  masses  constitutes  the  end-plate. 
The  involuntary  nonstriated  muscles  are  supplied  chiefly 
by  the  sympathetic  system.  These  nerve  fibres  form  plex- 
uses of  delicate  fibres  at  the  intersections  of  which  are  found 


86 


NERVOUS  TISSUES. 


ganglia  of  various  sizes.  Individual  branches  extend  to  the 
muscle  fibres  but  the  exact  manner  of  ending  is  not  under- 
stood. 

Neuromuscular  endings.  These  organs  are  spindle- 
shaped,  and  consist  of  4  to  20  small  voluntary  muscle  fibres, 
the  mtra-fusal  fibres,  surrounded  by  a  delicate  white  fibrous 
sheath,  the  atrial  sheath.    External  to  this  is  the  capsule  com- 


FiG.   33. — Motor  Nekve-endings   in    iNTEiicosiAL   Muscle   of  a  Rabbit. 


a.  Sensory  nerve  fibre ;   h.  muscle  fibres ;   c.  motor  plates ;  d.   medullated 
nerve  fibre;  e.  bundle  of  nerve  fibres  (Stohr^s  Histology). 

posed  of  about  six  layers  of  white  fibrous  connective  tissue 
concentrically  arranged  and  separated  from  the  axial  sheath 
by  a  lymph  space. 

In  the  equatorial  region  of  the  organ  the  muscle  fibres 
consist  chiefly  of  sarcoplasm  and  the  striations  are  faint, 
while  at  the  ends  the  striations  are  quite  distinct. 

One  or  more  medullated  nerve  fibres  enter  each  organ 
and  in  piercing  the  capsule  and  axial  sheath  divide  several 


TENDON-SPINDLES. 


87 


times.  As  each  branch  enters  the  axial  sheath  the  medullary 
sheath  ceases,  and  the  non-medullated  fibres  wind  around 
the  intrafusal  fibres,  and  end  in  small  terminal  knobs. 

These  organs  are  readily  visible  to  the  naked  eye,  measur- 
ing I  mm.  to  4  mm.  by  .1  mm.  to  .2  mm.  They  are  found  in 
greater  numbers  in  the  small  muscles  of  the  hand  and  foot. 


^ 


Fig.  34. — Tendon-spindle  of  a  Cat. 

&.   tendon    bundle ;    c.    muscle    fibres ;    d.    ter- 


Medullated   nerve   fibre 
minal  ramifications   (IStohr's  Histology). 


The  neurotendinous  endings  resemble  the  above  in  struc- 
ture, with  the  exception  that  the  intrafusal  fibres  are  tendon 
bundles  and  the  nonmedullated  fibres  do  not  wind  around  the 
intrafusal  fibres,  but  send  short  branches  that  end  in  little 
plates  upon  the  tendon  bundles. 


CHAPTER  VII. 


CIRCULATORY  SYSTEM. 

The  Circulatory  System  comprises  the  Heart,  Arteries, 
Capillaries,  V^ins  and  the  circulating  fluid,  the  Blood. 

THE  HEART. 

The  Heart  is  the  most  important  member,  as  on  its  con- 
tractions depends  the  circulation.  It  is  a  thick  muscular 
organ  composed  of  three  coats,  the  endocardium,  myocar- 
dium and  EPiCARDiUM. 

The  ENDOCARDIUM  consists  of  a  lining  of  endothelial  cells 
which  rest  upon  the  subendoihelial  (fibro-elastic)  tissue. 

The  endothelial  cells  are  flattened,  nucleated  plates  that 
have  an  irregular  outline  and  are  held  together  by  a  small 
amount  of  intercellular  cement.  They  differ  but  slightly  from 
those  found  within  the  vessels. 

The  snh endothelial  tissue  consists  of  a  network  of  white 
fibrous  and  yellow  elastic  tissues.  It  may  contain  a  few  in- 
voluntary nonstriated  muscle  fibres. 

Guarding  the  auriculo-ventricular  orifices  and  the  open- 
ings into  the  pulmonary  artery  and  aorta  are  duplications 
of  the  endocardium  called  valves.  Around  the  openings  the 
fibro-elastic  tissue  is  condensed  to  form  a  ring-like  mass,  the 
ANNULi  FiBROSi.    These  rings  serve  as  origins  for  the  valves. 

The  VALVES  consist  of  two  layers  of  endothelial  cells,  con- 
tinuous at  the  edges,  separated  by  the  subendothelial  tissue 
in  which  the  inelastic  tissue  predominates.  The  auricular 
muscle  may  extend  for  a  short  distance  into  the  auriculo- 
ventricular  valves.  The  chordae  tendineae  consist  of  cords 
of  fibrous  tissue  surrounded  by  endothelial  cells.  Above 
they  are  attached  to  the  valves  and  below  to  the  papillary 


HEART  89 

muscles.  The  semilunar  valves  possess  a  marginal  band 
with  a  central  enlargement,  the  corpus  Arantii.  The  band 
strengthens  while  the  corpus  ensures  complete  closure  of 
the  valves. 

The  MYOCARDIUM  consists  of  involuntary  striated  muscle. 
In  the  auricles  the  fibres  are  arranged  in  two  layers,  inner 
longiHidinal  and  outer  circular.  In  the  ventricles  the  fibres 
cannot  be  separated  so  distinctly  into  layers.  Some  run 
longitudinally,  others  transversely,  while  the  greatest  num- 
ber have  an  oblique,  circular,  or  spiral  course,  forming  even 
a  figure  eight.  Owing  to  this  arrangement  distinct  lamellae 
cannot  be  formed.  Usually  incomplete  internal  and  external 
longitudinal  layers  are  formed  between  which  are  seen  the 
circular  fibres  that  form  the  thickest  layer.  Besides  the 
latter  are  found  spiral  and  oblique  fibres  that  are  present 
chiefly  in  the  upper  and  lower  portions  of  the  left  ventricle. 

The  epicardium,  or  visceral  layer  of  the  pericardium. 
is  practically  a  duplication  of  the  endocardium  in  structure. 
It  consists  of  endothelial  cells  and  suh endothelial  tissue.  It 
differs  from  the  endocardium,  however,  in  being  separated 
from  the  myocardium  by  a  thin  layer  of  adipose  tissue  and 
in  possessing  no  muscle  fibres.  It  continues  up  over  the 
great  vessels  for  a  short  distance  and  is  then  reflected  over  a 
thick  sac  of  fascia,  with  which  it  constitutes  the  pericardial 
SAC,  or  the  parietal  layer  of  the  pericardium. 

The  blood-vessels  are  branches  of  the  coronary  arteries  and 
their  relation  to  the  muscle  fibres  has  been  described  under 
Muscular  Tissues.  The  endocardium  is  nourished  by  the 
blood  that  flows  over  it. 

Lymphatics  are  present  in  all  of  the  coats  but  do  not  com- 
municate with  one  another  to  any  great  extent. 

The  nerves  are  from  both  systems.  Sympathetic  ganglia 
are  numerous. 


go  CIRCULATORY   SYSTEM. 

The  blood  is  sent  from  and  returned  to  the  heart  by  the 
Vessels.  Of  these  there  are  three  varieties,  Arteries,  Capil- 
laries and  Veins. 

For  convenience  of  description,  Arteries  are  classed  as 
LARGE,  MEDIUM  and  SMALL.  The  LARGE  are  the  ^orta  and 
PULMONARY  ARTERY;  the  MEDIUM  the  remainder  of  the 
named  arteries  of  the  body,  and  the  small,  the  unnamed 
branches  that  gradually  become  capillaries.  All  have  the 
same  general  structure,  consisting  of  three  coats,  tunicas 

INTIMA,  MEDIA  and  ADVENTITIA. 

As  the  medium  sized  artery  is  the  type,  its  description  will 
be  considered  first  and  then  the  differences  between  It  and 
the  others  will  be  pointed  out. 

Medium  sized  artery.  The  tunica  intima,  or  interna, 
consists  of  three  layers,  the  endothelial,  sub  endothelial  and 
an  internal  elastic  lamina. 

The  endothelial  cells  differ  but  little  from  those  lining  the 
heart.  They  rest  upon  the  suh endothelial  Hhro-elastic  tissue. 
Limiting  this  coat  externally  is  a  prominent  wavy  band  of 
elastic  tissue,  the  internal  elastic  lamina,  which  does  not  take 
the  ordinary  stain  well,  and  appears  as  a  Hght  wavy  band. 

The  media  consists  chiefly  of  circularly  arranged  involun- 
tary nonstriated  muscle  tissue.  The  fibres  are  small  and 
closely  packed.  Elastic  fibres  in  moderate  quantities  are 
found  between  the  muscle  fibres  in  an  artery  of  this  size. 
Often  a  band  of  elastic  tissue  separates  this  layer  from  the 
adventitia.  This  is  the  external  elastic  lamina,  but  it  is 
neither  as  thick  nor  so  prominent  as  the  internal.  In  some 
vessels  (subclavian,  especially)  longitudinal  muscle  fibres 
are  seen  near  the  intima. 

The  ADVENTITIA,  or  EXTERNA,  is  a  thick  fibro-elastic  coat, 
and  protects  the  vessel  from  undue  dilatation.  In  some  ves- 
sels longitudinal  muscle  fibres  are  found.    This  coat  contains 


ARTERIES 


91 


the  larger  trunks  that  nourish  the  vessels,  the  vasa  vasonnn 
The  nervi  z'asoruin  are  present  also,  and  form  branches  that 
pass  to  the  muscular  coat. 

In  LARGE  ARTERIES  the  INTIMA  is  uot  SO  distinct  and  grad- 
d 


h 


Fig.  35. — Cross-section  op  a  Medium-sized  Artery. 

a.  Intiraa  ;  ft.  media ;  c.  adventitia ;  d.  endothelial  cells ;  e.  subendothelial 
tissue;  f.  internal  elastic  lamina;  g.  circular  muscle  tissue;  h.  elastic 
fibres  ;  i.  external  elastic  lamina ;  fc.  white  fibrous  tissue  ;  I.  arteriole ; 
m.  venule,   vasa  vasorum. 


ually  fades  into  the  media.  The  internal  elastic  lamina  is 
usually  not  present  as  such,  but  the  elastic  fibres  have  fused 
with  the  elastic  tissue  of  the  intima  to  form  the  fenestrated 
membrane  of  Henle.   The  media  is  not  very  muscular,  as  it 


92  CIRCULATORY   SYSTEM. 

contains  a  predominance  of  elastic  fibres  that  give  it  an  elas- 
tic, but  not  a  contractile,  character.  The  adventitia  differs 
but  slightly. 

In  SMALL  ARTERIES,  the  iutima  is  proportionately  thinner, 
and  the  elastic  lamina  quite  prominent  and  thick.  The  media 
is  proportionately  thicker  than  in  the  other  vessels.  It  con- 
tains very  little  elastic  tissue,  and  no  elastic  lamina. 

As  the  vessels  become  reduced,  the  intima  is  the  first  to 
suffer;  the  subendothelial  tissue  disappears,  and  the.  endo- 
thelial cells  are  seen  to  rest  upon  the  elastic  lamina.  The 
media  becomes  attentuated  so  that  only  a  single  layer  of 
muscle  fibres  is  seen.  This  soon  becomes  reduced  to  a  few 
stray  fibres.  The  adventitia  becomes  greatly  reduced,  and  is 
represented  by  a  few  bundles  of  fibrous  tissue.  This  is  prac- 
tically the  PRECAPILLARY  vcsscl.  It  is  succccdcd  by  the 
Capillary. 

The  Capillaries  are  merely  delicate  tubes  consisting  of  a 
single  layer  of  endothelial  cells  placed  end  to  end,  and  held 
together  by  intercellular  cement.  They  are  the  smallest  ves- 
sels, and  anastomose  freely  to  form  loose  or  dense  plexuses. 
At  times,  they  are  very  irregular,  possessing  dilatations. 
They  are  practically  very  thin  animal  membranes,  and 
through  their  walls  the  liquid  portion  of  the  blood  and  the 
ameboid'  white  blood  cells  have  no  difficulty  in  passing  into 
the  surrounding  tissues. 

In  muscles,  the  capillaries  run  parallel  to  the  course  of  the 
fibres,  and  are  connected  to  one  another  by  dilated  vessels, 
or  ampullae.  In  the  liver,  adrenal,  spleen  and  carotid  gland, 
the  endothelium  of  the  capillaries  is  usually  attached  to  the 
functionating  epithelium  or  parenchyma.  Such  vessels  are 
termed  sinusoids  (Minot).  In  the  kidney,  are  seen  little 
arterial  capillary  tufts  interposed  between  two  arterioles. 
Such  structures  are  termed  retia  mirabilia.     In  the  penis. 


VEINS. 


93 


the  arterioles  empty  into  cavernous  spaces,  or  sinuses  with- 
out forming  capillaries.  In  exposed  regions,  nose,  ear,  toes, 
kidneys  and  membranes  of  the  nervous  system,  direct  con- 
nection between  arteries  and  veins  exist.  They  are  called 
anastomoses. 

Veins  have  the  same  general  structure  as  arteries,  though 
the  coats  are  all  thinner,  and  collapse  more  readily. 

The  iNTiMA  often  shows  no  internal  elastic  lamina;  when 


A-^ 


-->b 


Fig.  36. — Portion  of  a  Cross-section  of  a  Human  Vein. 

A.  Intima ;  B.  Media ;  C.  Adventitia — a.  internal  elastic  lamina ;  &.  smooth 
muscle  fibres ;  c.  white  fibrous  connective  tissue ;  d.  smooth  muscle 
fibres  in  the  adventitia  {^tohr's  Histology). 


present,  it  is  not  prominent.  At  intervals,  this  coat  is  thrown 
into  folds  called  valves.  These  are  duplications  of  the 
intima,  and  are  usually  arranged  in  pairs.  At  the  place  in 
which  they  are  located,  the  vessels  are  usually  slightly 
dilated.  Valves  occur  only  in  the  veins  of  the  lower  e;c- 
tremities. 

The  MEDIA  contains  a  very  small  amount  of  muscle  tissue, 
but  is  reinforced  by  fibro-elastic  tissue.     In  some  veins,  the 


94  CIRCULATORY   SYSTEM. 

muscle  tissue  is  entirely  wanting  (brain  and  bones),  while 
in  oth-ers,  longitudinal  fibres  are  present  in  this  coat.  The 
lack  of  muscle  tissue  accounts  for  the  collapsibxlity  of  these 
vessels. 

The  ADVENTiTiA  is  the  most  prominent  coat,  and  may  pos- 
sess longitudinal  muscle  fibres.  It  is  similar,  in  structure, 
to  the  arteries. 

.Blood-vessels  are  nourished  by  vessels  that  pierce  the  ad- 
ventiti-a  and  send  branches  to  the  media,  the  vasa  vasorum. 
The  intima  is  nourished  by  the  blood  that  flows  over  it. 

The  NERVES  are  chiefly  sympathetic,  and  are  distributed 
to  the  media  and  adventitia.    They  are  the  nervi  vasorum. 

Vessels  are  often  the  centers  of  extensive  lymphatic  chan- 
nels that  lie  in  the  adventitia. 

The  Blood  is  the  only  liquid  connective  tissue.  It  is  com- 
posed  of   CELLULAR   ELEMENTS,   the    CORPUSCLES,    and    the 

INTERCELLULAR  SUBSTANCE,   the  LIQUOR   SANGUINIS. 

The  CELLULAR  ELEMENTS  are  of  three  varieties,  the  red 

CELLS,    WHITE   CELLS   and  PLATELETS. 

*The  RED  CELLS,  or  ERYTHROCYTES,  are  nonnucleated,  bj- .;*  > 
concave  discs   averaging   7.5   to  8.5   microns   in   diameter.  ^^ 
Under  the  microscope,  they  are  pale  straw  colored  or  green- 
ish.   Each  cell  consists  of  a  framework,  the  stroma,  that  con- 
tains the  hemoglobin.    The  latter  carries  the  oxygen. 

Some  cells  average  from  5.5  to  7.5  microns,  and  are 
called  microcytes,  while  those  over  8.5  microns  are 
macrocytes. 

In  normal  blood,  the  cells  tend  to  form  rolls,  or  rouleaux. 
Under  the  same  condition,  5,000,000  corpuscles  are  found, 
per  cubic  mm.,  in  the  male,  and  about  4,500,000  in  the  female. 

♦According  to  Lewis  of  Harvard,  the  normal  red  cells  are  hell-shaped 
and  the  biconcavity  is  due  to  collapse  that  occurs  upon  exposure  to  the 
air.     Rouleaux  are  readily  formed  by  these  cells  fitting  into  one  another. 


RED  BLOOD  CELLS. 


95 


Nucleated  red  cells,  or  erythroblasts,  are  found  in  the 
fetus,  in  bone-marrow  and  the  spleen.  The  cell  of  average 
size  is  called  a  normoblast,  the  smaller,  a  microhlast,  and  the 
larger,  a  macrohlast.  In  Ushes,  repiiles,  birds  and  amphib- 
ians, the  red  cells  are  nucleated.  In  all  mammals,  they  are 
circular,  except  in  the  camel  family,  in  which  they  are  oval. 
In  the  frog,  the  red  cells  are  very  large,  oval,  biconcave,  nu- 
cleated discs  that  are  far  larger  than  the  same  cells  in  man. 


F 


Fig.   37.— Blood-cells. 

A.  Platelets ;  B.  Leukocytes  :  C.  Leukocytes  in  motion  :  C\  Leukocyte  at 
rest;  D.  Red  cells  of  frog,  lateral  view.  1.  Red  cells  of  man  at  close 
focus;  2.  at  distant  focus;  3.  lateral  view  of  red  cells  (rouleaux). 
F.  Crenated  red  cells  of  man;  4,  5,  6.  red  cells  of  frog  {Stohr's  His- 
tology). 


The  size  of  the  red  cell  is  by  no  means  proportionate  to  that 
of  the  animal.  The  musk  deer  possesses  one  of  the  smallest 
(2.4  microns),  while  the  proteus  has  about  the  largest  (62.5 
microns).  That  of  the  elephant  is  but  9.2  microns  in  diam- 
eter, and  beside  it  stands  that  of  the  humming  bird,  with'  a 
diameter  of  nearly  9.4  microns. 

The  red  cells  are  more  numerous  in  carnivorous  than  in 
herbivorous  animals,  while  in  birds  they  are  larger  in  size. 


96  .  CIRCULATORY   SYSTEM. 

In  the  amphibians,  where  the  size  is  great,  the  number  is 
small. 

White  blood  cells,  or  leukocytes,  are  large,  pale  cells 
readily  distinguished  from  the  above.  About  5,000  to  8,000 
are  found  in  each  cubic  mm.  of  blood,  and  some  of  the 
varieties  have  the  powers  of  motion  and  phagocytosis. 

They  are  classified  as  follows : 

1.  Lymphocytes  (small  lymphocytes). 

2.  Hyalin  cells  (large  lymphocytes). 

3.  Polynuclear,  polymorphonuclear  leukocytes,  or 
FINELY  GRANULAR  OXYPHILS  {Formerly  n^eutrophil). 

4.  Coarsely  granular  oxyphils  (Formerly  acidophil), 

5.  Finely  granular  basophils. 

6.  Coarsely  granular  basophils. 


Fig.    38. — White    Blood-cells    of   Man. 

a.   Lymphocyte :    b.    poiymorplionuclear   cells ;    c.   finely   granular   oxyphil. 
X  600    {Stohr's   Histology). 


1.  The  LYMPHOCYTES  average  5  to  7  microns.  Each  con- 
sists of  a  large  darkly  staining  nucleus  surrounded  by  a 
narrow  rim  of  faintly  stained  protoplasm.  It  is  neither 
ameboid  nor  phagocytic  (though  this  is  now  in  doubt),  and 
constitutes  about  15  to  30  per  cent,  of  all  the  white  cells. 

2.  The  HYALIN  CELL  averages  11  to  15  microns.  Both 
nucleus  and  protoplasm  stain  but  faintly,  hence  the  name. 
It  is  actively  ameboid  and  phagocytic.  It  represents  2  to  6 
per  cent,  of  the  white  cells. 

3.  POLYNUCLEAR,  POLYMORPHONUCLEAR  LEUKOCYTES,  Or 
FINELY   GRANULAR    OXYPHILS,    ACIDOPHILS,    Or    EOSINOPHILS, 


I 


WHITE   BLOOD   CELLS.  97 

average  7.5  to  11  microns.  The  nucleus  has  many 
shapes,  as  U,  V,  W,  etc.,  and  may  even  be  divided  in  a  num- 
ber of  segments  (polynuclear).  The  protoplasm  contains  a 
number  of  fine  granules  that  take  the  acid  stain  deeply. 
These  granules  were  at  one  time  regarded  as  neutrophilic, 
and  the  cells  were  called  neutrophils.  They  are  actively  ame- 
boid and  phagocytic,  and  represent  60  to  y2  per  cent,  of  all 
leukocytes. 

4.  The     COARSELY     GRANULAR     OXYPHIL,     ACIDOPHIL,     Or 

EOSINOPHIL,  is  about  7  to  TO  microns  in  diameter.  The  proto- 
plasm contains  a  few  Large  granules  that  take  the  acid  stain 
deeply.  It  was  form-erly  called  acidophil,  or  eosinophil,  and 
is  actively  ameboid,  but  not  phagocytic.  It  represents  .1  to 
4  per  cent,  of  the  leukocytes. 

5.  The    FINELY   GRANULAR   BASOPHIL    reSCmblcS    GROUP    3, 

except  that  the  granules  take  a  basic  stain,  and  are  present  to 
the  extent  of  .i  to  i  per  cent. 

6.  The  COARSELY  GRANULAR  BASOPHIL  is  Said  to  be  absent 
from  normal  blood.  It  is  a  relatively  large  cell,  and  is  also 
called  the  mast  cell. 

Another  cell  that  is  usually  described  among  the  leukocytes 
is  the  myelocyte,  or  marrow  cell.  This  cell  is  not  a  normal 
constituent  of  the  blood,  but  is  found  there  in  certain  blood 
diseases. 

The  BLOOD  PLATELETS  are  small  (2  to  4  microns),  oval  or 
circular  discs,  capable  of  ameboid  movement.  They  number 
about  200,000  to  300,000  per  cubic  mm.  Their  function  and 
origin  are  unknown. 

The    INTERCELLULAR    SUBSTANCE,     Or    LIQUOR    SANGUINIS, 

contains  the  salts  of  the  blood.  Its  density  is  such  that  the 
cells  retain  their  normal  shape.  If,  however,  solutions  are 
added  that  differ  in  density,  the  action  upon  the  cells  is  char- 
eteristic. 

h 


98 


CIRCULATORY   SYSTEM. 


Upon  the  addition  of  salt  solution,  the  cells  become  irregu- 
lar in  outline,  and  are  crenated.  If  water  be  added,  it  dis- 
solves the  hemoglobin,  and  the  cells  swell  and  become  spheri- 
cal, but,  as  a  rule,  are  not  destroyed. 

The  action  of  acetic  acid  is  important.  The  addition  of  a 
.3  per  cent,  solution  decolori:;es  the  red  cells  and  renders  the 
white  cells  more  distinct.  This  is  made  use  of  in 
Hematology  for  the  purpose  of  counting  the  white  cells,  in 
a  fresh  condition. 

When  blood  clots,  fibrin  is  precipitated,  and  this  entangles 
the  corpuscles. 


1.  Hemin  crystals  of  man  (x  560)  ;  2.  crystals  of 
common  salt :  3.  hematoid  crystals  of  man 
(Stohr^s  Histology). 


40.  —  Hemoglo- 
Crystals  of  a 
Dog  (x  100) ;  a 
crystal  Separating 
into  fibres  (Stohr's 
Histology). 


Hemoglobin  is  an  organic  compound  of  iron,  and,  as  it  - 
exists  in  the  blood,  it  cannot  be  readily  studied.     Its  conver- 
sion into  the  crystallin  state  is  not  difficult. 

Hemoglobin  crystals  will  be  formed  if  a  drop  of  de- 
fibrinated  blood  be  mixed  with  a  drop  of  Canada  balsam,  or 
clove  oil,  and  covered  with  a  cover-glass.  They  are  large, 
red,  tetrahedral  crystals. 

Hemin  crystals  may  be  prepared  by  adding  a  small 
crystal  of  salt  and  two  drops  of  glacial  acetic  acid  to  a  little 
dried  blood,  and  heating  until  the  mixture  boils.  During  this 
process,  it  should  be  covered.  When  cool,  small  brownish 
crystals  will  be  found.     These  may  be  single  or  grouped  in 


HEMAL   GLANDS  99 

the  form  of  rosettes,  and  are  known  as  Teichmann's  crystals. 

Among  the  blood-making  organs  are  placed  the  coccygeal 
and  CAROTID  glands. 

The  former,  luschka^s  gland,  is  found  in  front  of  the 
coccyx,  and  is  joined  to  the  middle  sacral  artery.  It  is  sur- 
rounded by  a  fibrous  sheath,  which  sends  in  septa  that  divide 
the  organ  irregularly  into  areas,  or  compartments.  The 
latter  contain  groups  of  polyhedral  cells  surrounded  by  dense 
plexuses  of  capillaries.  Nonmedullated  nerve  fibres  are 
numerous. 

The  CAROTID  GLAND  is  fouud  at  the  bifurcation  of  the  com- 
mon carotid  artery,  and  its  structure  is  the  same  as  that  of 
Luschka's  gland. 


CHAPTER  VIII. 


THE  LYMPHATIC  SYSTEM. 

The  Lymphatic  System  includes  the  lymphatic  and 
thoracic  ducts,  capillaries  and  intermediate  vessels,  and  a 
number  of  organs,  Lymph  Node  (Lymphatic  Gland), 
Spleen  and  Thymus  Body. 

The  ducts  resemble  veins  more  than  arteries.  Their  walls 
are  thin,  and  they  possess  valves.  The  arrangement  of  the 
muscle,  and  the  distribution  of  the  nerves,  are  like  those  of 
an  artery. 

Lymph  capillaries  are  much  larger  than  those  of  the 
vascular  system,  measuring  30  to  60  microns  in  diamiCter. 

Lymphoid   tissue    is    arranged    in    four   ways,   diffuse, 

SOLITARY     FOLLICLES,      AGMINATED     FOLLICLES     and     LYMPH 

NODES,  or  LYMPHATIC  GLANDS.  The  first  three  have  been 
considered  under  Adenoid  Tissue.  (See  Connective  Tis- 
sues,  p.    59). 

Lymph  Nodes,  or  Glands,  are  small,  bean-shaped  organs, 
surrounded  by  a  capsule,  and  composed  of  cortex,  me- 
dulla and  HiLus. 

The  capsule  consists  of  white  fibrous  tissue,  and  is  ar- 
ranged in  two  layers,  enclosing  a  lymph  space.  From  its 
inner  surface,  traheculae  are  ^ent  into  the  cortex,  and  these 
divide  the  latter  into  a  number  of  masses  called  secondary 
follicles,  or  nodules.  The  lymph  space  continues  along  the 
traheculae. 

The  CORTEX  contains  the  secondary  nodules  and  traheculae. 
The  former  consist  of  dense  adenoid  tissue,  and  contain  a 
germinal  center.  The  cells  are  chiefly  lymphocytes,  which 
are  arranged  in  concentric  layers  around  the  periphery. 
Other  cells  of  the  hyalin  variety  are  found  in  the  central  por- 


LYMPH   NODE.  lOI 

tion.  During  gestation,  nucleated  red  cells  may  be  present. 
The  follicles  continue  into  the  center  of  the  node  as  the  me- 
dullary cords. 

The  irabcc  III  a  e  sepd.v  Site  the  follicles  from  one  another, 
and  pass  into  the  medulla  surrounded  by  the  lymph  space. 

The  MEDULLA  consists  of  the  medullary  cords  and 
trabeculae.  Z^:^'"    - 


(; 


I 


Fig.    41. — Longitudinal    Section    of   a   Lymph    Node. 

a.  Hilus  ;  b.  arteriole  ;  c.  venous  sinuses  ;  d.  adipose  tissue  ;  e.  secondary 
nodule  of  cortex ;  /".  vein  medulla ;  g.  subcapsular  lymph  sinus : 
li.  germinal  center  of  secondary  nodule  ;  i,  i.  trabeculae  ;  k.  capsule  ; 
I.  lymph  sinus ;  m.   medullary  cord. 

The  cords  are  the  band-like  continuations  of  the  secondary 
follicles,  and  are  separated  from  the  trabeculae  by  the  lymph 
spaces  that  accompany  the  latter.  They  consist  of  dense 
adenoid  tissue,  supported  by  reticulum.     At  the  hilus,  the 

edulla  comes  to  the  surface. 

The  HILUS  is  a  scar-like  depression  at  one  side,  where 
the  vessels  enter  and  leave.  At  this  place,  the  secondary 
^nodules  are  wanting,  and  the  medulla  comes  to  the  surface. 


I02  THE   LYMPHATIC   SYSTEM. 

The  arterial  vessels,  to  a  great  extent,  enter  at  the  peri- 
phery of  the  node.  Their  branches  continue  into  the  trabe- 
culae,  and  then  pass  into  the  folHcles.  Those  that  enter  at 
the  hilus,  also  follow  the  trabeculae,  and  bridge  the  sinuses 
to  enter  the  lymphoid  tissue. 

The  venous  radicals  all  pass  toward  the  hilus,  where  one 
or  more  vessels  may  be  formed  that  carry  all  the  blood  away 

The  afferent  lymph  vessels  pierce  the  capsule  at  different 
points,  and  empty  into  the  capsular  sinus.  The  lymph  passes 
down  along  the  trabeculae,  and  filters  through  the  organ. 
All  the  lymph  is  collected  into  one  or  more  afferent  vessels 
that  leave  at  the  hilus. 

Lymph  nodes,  or  glands,  are  the  highest  form  of  lymphoid 
tissue.  They  are  scattered  throughout  the  lymphatic  system, 
in  the  pathways  of  the  vessels.  They  are  often  collected 
into  groups,  as  in  the  axillary,  inguinal  and  femoral  regions 

Lymphatic  glands  are  uncertain  structures,  as  they  may 
disappear  early,  or  change  from  place  to  place.  They  make 
the  white  blood  cells,  filter  the  lymph,  are  the  centers  of  cell 
destruction,  and  may  possibly  give  rise  to  red  blood  cells. 

SPLEEN. 

The  Spleen  is  a  lymphoid  structure,  surrounded  by  a 
capsule  of  dense  white  fibrous  tissue  that  contains  involun- 
tary nonstriated  muscle  fibres,  and  limits  the  splenic  sub- 
stance. 

The  capsule  sends  in  trabeculae  that  divide  the  organ  ir- 
regularly into  compartments.  At  one  side,  is  a  depression, 
the  HILUS,  at  which  the  vessels  enter  and  leave. 

The  splenic  substance  consists  of  two  main  portions,  the 

PULP  and   MALPIGHIAN   CORPUSCLES. 

The  PULP  is  composed  of  diffuse  adenoid  tissue,  broken 
down  red  cells,  nucleated  red  cells  and  some  large  polynu- 


SPLEEN  103 

clear  elements.  To  the  red  cells  the  peculiar  color  is  due,  and 
the  organ  has  been  called  the  "grave-yard  of  the  red  cells." 
The  cells  are  supported  by  retiform  connective  tissue. 

The  MALPiGHiAN  CORPUSCLES  are  solitary  follicles  and 
consist  of  dense  adenoid  tissue.  They  differ  from  the  ordi- 
nary follicle  in  possessing  an  eccentrically-placed  arteriole. 


^ 


^  -!*~>'rLrt, 


^'^i^c- 


Fig.   42. — Section   of   Spleen. 

a.  Capsule ;  b.  trabeculae  longitudinal  section ;  c.  pulp ;  d.  Malpighian 
corpuscle ;  e.  germinal  center  of  corpuscle ;  jf.  eccentric  arteriole  in 
corpuscle  ;  g.  trabecula  cross  section  ;   U.  blood-vessel. 


This  adenoid  tissue  is  held  to  be  in  the  adventitial  sheath  of 
the  arteriole,  and  forms  a  spherical  mass  at  the  bifurcation 
of  the  vessel.  These  follicles  usually  show  germinal  centers. 
The  circulatory  system  of  the  spleen  is  peculiar  in  being 
an  open  one.  Capillaries,  as  such,  do  not  exist,  and  the 
arterioles  and  venules  are  connected  by  blood  spaces,  or 
ampullae. 


I04  THE   LYMPHATIC    SYSTEM. 

The  splenic  artery  enters  at  the  hilus,  and  breaks  into 
branches  that  follow  the  trabeculae.  Of  these,  some  quickly 
pass  into  the  pulp,  while  others  follow  the  trabeculae  to  their 
smallest  divisions.  The  spleen  is  divided  into  lobules,  about 
one  mm.  in  diameter,  each  one  of  which  is  further  subdivided 
into  histologic  units,  one  for  each  terminal  artery,  or  am- 
pulla. These  terminal  vessels  are  covered  by  a  lymphatic 
sheath,  the  ellipsoidal  sheaths.  The  terminal  ampullae  are 
porous,  and  continue  as  veins. 

The  spleen  is  subject  to  rhythmic  contractions,  one  per 
minute,  and  about  i8  per  cent,  of  its  volume  is  lost  at  each 
contraction.  These  are  produced  by  the  involuntary  muscle 
in  the  capsule  and  trabeculae.  When  the  cardiac  impulse 
sends  the  blood  into  the  arteries,  the  blood  passes  into  the 
ampullae,  and  through  the  porous  walls  into  the  pulp.  When 
the  rhythmic  contractions  occur,  the  blood  is  forced  into  the 
veins,  and,  at  the  same  time,  the  arteries  are  closed.  This 
shows  an  open  circulation  (Mall). 

Lymphatics  occur  in  the  capsule  and  trabeculae  only. 

THYMUS  BODY. 

The  Thymus  Body  is  essentially  a  lymphoid  structure, 
though  it  undergoes  peculiar  changes  in  its  life's  history. 

It  originates  as  a  true  gland  (epithelial  organ),  but  soon 
leukocytes  infiltrate  it,  and  cause  the  disappearance  of  the 
epithelium,  except  small  islands.  After  the  sixth  year,  it 
generally  undergoes  further  change.  The  lymphoid  tissue 
is  gradually  replaced  by  adipose  tissue,  so  that  an  old  thymus 
will  show  but  little  adenoid  tissue. 

This  organ  is  surrounded  by  a  capsule  of  white  fibrous 
tissue  that  sends  in  septa,  which  divides  the  organ  into 
LOBES  and  lobules. 

Each  lobule  consists  of  cortex  and  medulla. 


THYMUS  BODY 


105 


The  CORTEX  is  composed  of  dense  lyiuplioid  tissue,  and 
stains  deeply,  owing  to  the  large  number  of  leukocytes  pres- 
ent. The  MEDULLA  consists  of  diffuse  adenoid  tissue,  and 
takes,  therefore,  a  lighter  stain.  The  supportive  tissue  is 
retieulinii. 

In  the  medulla,  are  found  small,  peculiar  bodies,  consisting 
of  concentrically  arranged  epithelial  cells ;  these  are  the  cor- 


Ftg.  43. — Section  of  the  Thymus  Body  of  a  Child. 

a.  Capsule  ;  h.  interlobular  connective  tissue  ;  c,  c.  adipose  tissue  ;  d.  blood- 
vessels in  interlobular  tissue ;  e.  cortex ;  f.  medulla ;  g.  blood-vessel 
in  lobule;  h,  h.  corpuscle  of  Hassal  ;  *.  corpuscle  of  Ilassal  magnified. 


piiscles  of  Hassal.  They  are  supposed  to  represent  the  re- 
mains of  the  epithelium,  though  some  hold  that  they  repre- 
sent endothelium  of  blood-vessels.  These  bodies  are  encap- 
sulated, and  may  be  compound. 

The  blood-vessels  pierce  the  capsule,  and  form  branches  in 
the  interlobular  connective  tissue.  From  these,  capillaries 
enter  the  lobules  and  are  distributed  to  the  adenoid  tissue. 


CHAPTER  IX. 


ALIMENTARY  TRACT. 

The  Alimentary  Tract  starts  at  the  Hps,  and  extends  to 
the  anus.  It  receives  the  food,  digests  it  and  casts  off  that 
which  is  undigested.  The  various  portions  perform  different 
functions,  and  the  lining  cells  differ  accordingly.  The  inner 
coat  is  a  mucous  membrane  that  gives  rise  to  glands,  which 
are  devices  of  nature  for  increasing  the  secretory  sur- 
face. The  absorptive  surface  is  increased  by  prolongations 
of  the  mucosa  into  the  lumen  of  the  organ  (villi  of  the  small 
intestine). 

The  Lip  is  covered  externally  by  skin^  and  internally  by 
MUCOUS  MEMBRANE.  Between  these,  are  found  connective 
tissue  and  muscle. 

The  SKIN  consists  of  two  portions,  the  epithelial,  or  epi- 
dermis, and  the  connective  tissue  portion,  or  derma. 

The  epidermis  is  composed  of  stratified  squamous  cells, 
of  which  two  layers,  the  stratum  corneum  and  stratum  Mal- 
pighii  are  distinct.  The  stratum  corneum  is  the  outer,  and 
consists  of  nonnucleated  scales;  the  stratum  Malpighii  is 
the  genetic  portion.  Its  lowest  cells  rest  upon  a  basement 
membrane,  and  are  columnar  in  shape.  Those  above  are 
polyhedral ;  the  latter  become  more  flattened  as  the  corneum 
is  approached.  The  derma  consists  of  white  fibrous  connect- 
ive tissue  supporting  blood-vessels,  nerves  and  lymphatics. 
Beneath,  the  epithelium  it  is  thrown  into  waves  called 
•papillae. 

The  mucous  surface  is  also  lined  by  stratified  squamous 
cells,  that  differ  from  the  outer,  however,  in  being  larger 
and  less  readily  stained.  The  cells  rest  upon  a  basement 
membrane,  beneath  which  is  the  tunica  propria,  composed  of 
papillated,  delicate  white  fibrous  tissue. 

io6 


TEETH.  107 

Between  the  tunica  propria  and  skin,  are  found  connective 
tissue  and  voluntary  striated  muscle.  Near  the  tunica  pro- 
pria, are  to  be  seen  small,  compound  tubular  glands  that 
open  upon  the  mucous  surface.  At  the  margin  of  the  lip 
these  two  surfaces  join,  and  this  is  the  miico-ciiiancous  junc- 
tion; here  the  epithelial  layer  is  quite  thick,  and  the  cells 
are  larger  and  bladder-like,  resembling  the  epitrichial  cells 
of  the  fetus. 

Blood-vessels  are  found  in  great  abundance,  and  form 
dense  plexuses,  especially  around  the  glands. 

The  Mouth  is  Hned  by  a  mucous  membrane,  consisting 
of  siratiiled  squamous  cells  resting  upon  a  basement  mem- 
brane and  tunica  propria.  Here  and  there  are  found  small 
glands  of  the  sam.e  nature  as  those  found  in  the  lips. 

THE  TEETH. 

The  Teeth  have  a  peculiar  structure.  Each  consists  of  a 
portion  that  extends  beyond  the  gum,  the  crown;  and  a  por- 
tion passing  into  the  jaw,  the  root,  or  fang.  Between  these, 
is  a  narrow  part  covered  by  the  gum,  the  neck.  The  fang  is 
covered  by  a  fibrous  membrane,  the  periodontal  membrane. 
Within  the  tooth,  is  a  space  called  the  pulp  cavity. 

The  CROWN  is  the  exposed  portion,  and  is  covered  by  the 
enamel,  which  is  thinnest  at  the  neck,  but  increases  in  thick- 
ness as  the  summit  is  reached.  The  enamel  is  composed  of 
peculiarly  modified  epithelial  cells,  the  adamantoblasts,  or 
amelioblasts  that  have  become  changed  to  the  hardest  sub- 
stance in  the  body.  Each  cell  is  columnar,  and  becomes  con- 
verted into  enamel  from  within  outward,  assuming  the  shape 
of  a  prism.  These  prisms  are  thinner  at  their  inner  ends, 
and  are  arranged  in  bundles  that  are  perpendicular  to  the 
surface  of  the  dentin  beneath.  The  various  bundles  are, 
however,  not  parallel  to  one  another. 


io8 


ALIMENTARY    TRACT. 


The  CEMENTUM,  or  CRUSTA  PETROSA,   extends   from  the 
enamel  to  the  base  of  the  tooth.    It  is  a  narrow  layer  of  bonv 


■  5 
Fig.  44. — Longitudinal  Section  of  an  Incisor  Tooth. 
A.  Crown;  B.  Neck;  C.  Fang;  1.  enamel;  2.  dentin;  3.  pulp-cavity;  4.  ce- 
mentum ;   5.  root-canal    {after  Stohr's  Histology). 

substance,   thickest   at   the  base,   and   containing,   here   and 
there,  quite  a  number  of  laaifiae,  canaliculi  and  osteoblasts. 


i 


TEETH.  109 

The  basal  portion  is  pierced  by  a  small  canal,  root  canal, 
through  which  the  nerve  and  vessels  enter  the  tooth. 

The  DENTIN  is  found  beneath  the  enamel  and  cementum, 
and  forms  the  bulk  and  shape  of  the  tooth.  It  is  an  ivory- 
like substance,  formed  by  the  odontoblasts,  and  consists  of 
a  great  number  of  tubules  that  extend  from  the  pulp  cavity 
to  the  enamel  and  cementum.  Each  tubule  consists  of  more 
compact  material  than  the  intervening  portions,  and  for  this 
reason  are  called  dentinal  tubules,  or  sheaths;  the  inter- 
vening portions  are  the  intertubular  dentin.  The  canals 
within  the  tubules  have  a  greater  diameter  near  the  pulp 
cavity  than  peripherally,  and,  as  they  pass  outward,  give  off 
branches  that  communicate  with  the  other  tubules.  The 
canals  contain  processes  of  the  odontoblasts  that  extend  out- 
ward as  the  dentinal  fibres.  Beneath  the  enamel  these 
canals  pass  through  spaces,  in  which  dentin  failed  to  form 
but  which  are  filled  by  a  soft  substance,  and  are  known  as 
the  interglobular  spaces.  At  the  cementum,  the  canals  end 
blindly.  Here  are  found  a  series  of  smaller  spaces  called 
Tomes'  granular  layer.  The  inter Uibular  dentin  has  a  fibril- 
lar structure. 

The  dentin  may  be  looked  upon  as  a  modified  bone,  in 
which  cell-spaces,  or  lacunae,  are  absent,  but  in  which  the 
canaliculi  are  represented  by  the  dentinal  canals. 

Enamel  and  dentin  start  to  form  at  the  same  line,  but  while 
the  enamel  is  formed  from  within,  outward,  the  dentin 
is  laid  down  from  without,  inward. 

The  PULP  CAVITY  is  a  space  within  the  tooth  that  has  not 
been  encroached  upon  by  the  dentin.  In  the  living  condi- 
tion, it  is  filled  by  the  pulp.  This  is  a  highly  sensitive  vas- 
cular tissue,  composed  chiefly  of  the  white  fibrous  variety, 
which  supports  the  vessels  and  nerves  that  penetrate  through 
the  root  canal.  Separating  it  from  the  dentin,  is  a  row  of 
DONTOBLASTS^  which  are  modified  pulp  cells. 


no  ALIMENTARY    TRACT. 

The  ODONTOBLASTS  are  very  tall  columnar,  or  pyramidal 
cells  whose  bases  are  closely  applied  to  the  dentin.  From 
the  bases,  the  dentinal  -fibres  pass  into  the  canals.  The  apex 
usually  receives  a  branch  of  a  nerve  fibre. 

Separating  the  tooth  from  the  bony  socket,  is  a  thick 
membrane,  the  periodontal,  or  alveolar  membrane.  .  This 
is  practically  a  periosteum,  as  upon  both  surfaces  osteoblasts 
are  present.  Those  upon  the  tooth  side  form  the  cementum, 
while  those  upon  the  socket  surface  aid  in  forming  the  jaw. 
The  intervening  portion  consists  of  white  fibrous  connective 
tissue,  of  which  many  fibres  have  a  transverse  course.  These 
correspond  to  Sharpey's  fibres,  as  they  pass  into  the  cement- 
um and  the  jaw.  The  membrane  is  continuous  with  the 
tunica  propria  of  the  gum. 

THE  TONGUE. 

The  Tongue,  like  the  Teeth,  occupies  part  of  the  mouth 
cavity.  It  is  covered  by  a  mucous  membrane  that  consists 
of  stratified  squamous  cells,  basement  membrane  and  tunica 
propria,  which,  along  the  sides  and  base,  is  papillated.  The 
upper  surface,  or  dorsum,  is  characteristic.  Its  anterior  two- 
thirds  is  covered  by  minute  projections,  called  papillae;  of 
these  there  are  three  varieties,  filiform,  fungiform  and 
circumvallate.  The  central  portion  consists  chiefly  of 
voluntary  striated  muscle. 

The  FILIFORM  PAPILLAE  are  cone-shaped  projections  of 
the  tunica  propria,  covered  by  the  stratified  squamous  cells, 
the  outer  ones  of  which  are  hard  and  horny.  The  central 
part  of  a  papilla  consists  of  white  fibrous  tissue,  which  is 
thrown  into  small  secondary  papillae  that  are  not  visible  ex- 
ternally These  papillae  are  the  most  numerous,  and  are 
scattered  over  the  whole  of  the  anterior  two-thirds.  They 
are  directed  backward,  and  are  the  ones  that  produce  the 


TONGUE.  Ill 

scratching  sensation  when  the  hand  is  Hcked  by  a  lower 
animal. 

The  FUNGIFORM  PAPiLLiAE  are  flat-topped,  table-like 
structures,  in  which  the  sides  are  parallel.  They  have  sec- 
ondary papillae,  and  are  scattered  like  the  filiform  variety, 
but  are  less  numerous. 

The  ciRCUMVALLATE  PAPILLAE  are  the  most  important. 
While  the  top  is  flat,  the  sides  usually  converge  and  give  this 
variety  a  narrow  base,  secondary  papillae  are  found  only 
on  the  upper  portion.  Each  papilla  is  surrounded  by  a  little 
vallum,  or  ditch,  hence  the  name. 

These  papillae  are  the  least  numerous,  and  are  found 
only  in  one  area.  Ten  to  fifteen  arrange  themselves  like  a 
letter  V,  with  the  apex  at  the  foramen  cecum,  a  little  de- 
pression that  lies  at  the  boundary  of  the  anterior  two-thirds 
and  posterior  one-third  of  the  tongue.  These  papillae  con- 
tain TASTE-BUDS  along  their  sides. 

The  TASTE-BUDS  are  the  end  organs  of  taste,  lie  in  the 
epithelial  portion  of  the  sides,  and  have  a  definite  structure. 
They  are  barrel- shaped,  and  open  at  the  exposed  ends.  Each 
consists  of  two  kinds  of  cells,  outer  (stave-like),  the  susten- 
tacular,  or  supporting  cells,  and  the  inner,  neuro-epithelial 
elements. 

The  SUSTENTACULAR  cclls  are  flat  and  stave-like  elements 
possessing  a  prominent  nucleus.  The  neuro-epithelial  ele- 
ments are  spindle-shaped,  and  each  ends  in  a  minute,  hair- 
like process,  the  gustatory  hair,  that  projects  through  an 
opening  in  the  barrel,  the  gustatory  pore.  The  nerve  fibre 
that  extends  to  each  bud  forms  branches,  one  of  which  is  sup- 
plied to  each  neuro-epithelial  cell. 

Beneath  the  mucosa  is  found  the  musculature  of  the 
tongue.  This  consists  of  the  voluntary  striated  variety,  ar- 
ranged   longitudinally,    vertically    and    transversely.      The 


IT2 


Ai:iMKNTARY    TRACT. 


"'W'    k/r* 


ist^giii^ 


Fig.   45. — Cross-section   of  Tongue. 

a.  Stratifiec:  squamous  cells :  h.  basement  membrane :  c.  tunica  propria ; 
d.  serous  glands  :  e.  mucous  glands  ;  f.  venule  :  g.  longitudinal  muscle 
fibres ;  h.  vertical  muscle  fibres ;  i.  transverse  muscle  fibres ;  I.  sep- 
tum :  m.  filiform  papilla ;  n.  secondary  papillae ;  r.  adipose  tissue. 
A.  Filiform  papilla.  B.  Fungiform  papilla.  (".  D.  (^ircumvallate 
papillae — m,  m.  taste  buds  ;  n,  n.  glands.  E.  Taste  bud — o.  nucleus 
of  neuro-epithelial  cell  ;  r.  nerve  fibre ;  s.  gustatory  hair ;  t  susten- 
tacular   cell ;   v.   neuro-epithelial   cell. 


TONSILS  113 

longitudinal  fibres  are  arranged  in  bundles  that  lie  beneath 
the  tunica  propria  and  extend  around  the  tongue.  They  are 
separated  by  small  bundles  of  vertical  fihres.  In  the  center, 
the  fibres  are  vertical,  oblique  and  transverse,  and  are  separ- 
ated in  the  middle  line  by  a  little  partition,  or  septum.  This 
consists  of  white  fibrous  tissue,  and  arises  at  the  base,  but 
does  not  reach  the  tip.  It  varies  in  height,  being  higher  in 
the  middle  than  at  either  end.  In  the  muscular  portion, 
small  glands  are  often  found.  Occasionally,  branched 
muscle  fibres  are  fotmd. 

The  true  hose  of  the  tongue,  the  posterior  one-third,  pos- 
sesses no  papillae.  It  contains  small  salivary^  glands  and 
collections  of  adenoid  tissue  called  the  lingual  tonsils' 

The  blood-vessels  are  quite  numerous;  the  capillaries  ex- 
tend into  the  papillae  and  between  the  muscle  fibres  and  form 
plexuses  around  the  glands. 

The  lymphatics  are  in  the  base,  and  are  found  quite  numer- 
ous in  the  tunica  propria,  where  they  receive  branches  from 
the  papillae. 

THE  TONSILS. 

The  Tonsils  are  found  just  between  the  mouth  and 
pharynx,  and  are  essentially  lymphoid  structures. 

They  are  covered,  upon  their  exposed  surface,  by  strati- 
fied squamous  cells  that  dip  down  into  the  organ  in  the  form 
of  irregular  tubes  called  the  tonsillar  crypts.  The  organ  is 
separated  from  the  surrounding  tissue  by  a  layer  of  white 
fibrous  tissue,  the  capsule,  that  sends  in  trabeculae,  which 
form  the  main  frame-work  of  the  organ.  The  bulk  of  the 
tonsil  consists  of  adenoid  tissue,  in  the  form  of  the  diffuse 
variety  and  solitary  follicles.  The  latter  show  germinal  cen- 
ters, and  are  found  chiefly  around  the  crypts.  The  support- 
ive tissue  is  of  the  retiform  variety.     Leukocytes  may  be 


114  ALIMENTARY    TRACT. 

seen  on  their  way  to  the  crypts,  where  they  become  the  sal- 
ivary  corpuscles. 

Blood-vessels,   and   especially   lymphatics,  are  numerous. 
The  vascular  capillaries  ramify  the  adenoid  tissue,  while  the 


^^:  i:^'?::!!^^^^^^ 


l^- ' 


Fig.    46. — Vertical   Section    of    Human   Tonsil. 
a.  Stratified  squamous  epithelium  ;   ft.  basement  membrane ;  c.  tunica  pro- 
pria ;   d.   trabeculae ;   e.   diffuse   adenoid   tissue ;    f.   adipose  tissue ;    h. 
capsule ;  i.  glands ;  k.  muscle ;  I.  blood-vessel ;  m.  epithelium  of  crypts ; 
q,  q.  crypts. 

lymph  channels  surround  the  follicles  and  form  a  peripheral 
vessel  beneath  the  fibrous  capsule. 


THE  PHARYNX. 

The  Pharynx  is  a  musculo-membranous  bag  that  con- 
nects the  mouth  cavity  and  the  esophagus.  It  has  three 
coats,  MUCOUS,  FIBROUS  and  muscular. 

The  MUCOUS  coat  is  lined,  in  the  lower,  or  alimentary, 
portion,  by  stratified  squamous  cells,    The  upper,  or  respira- 


ESOPHAGUS.  115 

tory,  part  is  lined  by  stratiHed  ciliated  cells.  These  all  rest 
upon  a  basement  membrane,  beneath  which  is  the  tunica 
propria,  that  is  thrown  into  waves  or  papillae.  The  tunica 
propria  contains  a  considerable  amount  of  diffuse  adenoid 
tissue. 

The  FIBROUS  COAT  is  composed  of  large  bundles  of  white 
fibrous  tissue,  and  serves  as  a  support  to  the  larger  vessels 
and  the  small  pharyngeal  glands.  It  also  serves  as  an  attach- 
ment for  the  muscle  fibres. 

The  MUSCULAR  COAT  consists  of  voluntary  striated  muscle, 
surrounded  externally  by  loose  areolar  tissue. 

The  blood-vessels  and  lymphatics  are  numerous.  The  cap- 
illaries are  found  in  the  mucous  and  muscular  coats,  around 
the  glands  and  between  the  muscle  fibres. 

ESOPHAGUS. 

The  remainder  of  the  Alimentary  Tract  is  tubular,  and 
possesses  four  coats,  mucous,  submucous,  muscular  and 
FIBROUS.  The  MUCOSA  is  further  subdivided  into  four  layers, 
epithelium,  basement  membrane,  tunica  propria  and  muscu- 
laris  mucosae. 

In  the  Esophagus,  the  mucous  coat  is  lined  by  stratiHed 
squamous  cells.  These  rest  upon  the  basement  membrane, 
beneath  which  is  the  papillated  tunica  propria.  The  latter 
consists  of  yellow  elastic  and  white  fibrous  tissues,  in  which 
the  capillary  vessels  form  a  delicate  network  beneath  the 
epithelium ;  the  ducts  of  the  glands  pass  through  this  layer 
on  their  way  to  the  surface.  The  mujcularis  mucosae  con- 
sists of  involuntary,  nonstriated  miiscle  fibres^,  ok^cularl^L-and 
longitudinally  arranged.  In  the  upper  portion  of  the  esopha- 
gus, this  layer  is  often  wanting,  but  in  the  lower  part  it  is 
always  present.  In  the  relaxed  condition,  the  mucous  and 
submucous  coats  are  thrown  into  longitudinal  folds. 


^K 


ii6 


ALIMENTARY    TRACT. 


The  SUBMUCOUS  coat  is  composed  of  coarser  bundles  of 
white  fibrous  tissue,  which  forms  a  loose  network  for  the 
support  of  the  large  blood-vessel  trunks.  In  this  coat  are 
seen    a    number    of    glandular    structures,    the    esophageal 


%( 


6 


'4 


Fig.    47. — Cross-section    Esophagus. 

a.  Stratified  squamous  epithelium  ;  Z>.  basement  membrane  ;  c.  tunic  pro- 
pria ;  d.  muscularis  mucosae ;  e.  esophageal  gland ;  f.  blood-vessel  ; 
(J.  submucosa  :  fc.  outer  longitudinal  muscle  ;  I.  fibrous  coat ;  n.  inner 
circular  muscle. 


glands,  which  are  apparently  mucous,  as  they  stain  lightly 
They  send  their  ducts  through  the  mucous  coat.  As  the 
stomach  is  approached,  these  glands  become  more  numerous, 
and  may  even  be  found  in  the  mucosa. 


STOMACH  11/ 

The  MUSCULAR  COAT  consists  of  muscle  fibre,  arranged  in 
two  layers,  inner  circular  and  outer  longitudinal.  In  the 
upper  third,  these  fibres  are  of'the  voluntary  striated  y?^^^^ 

in  the  lower  third,  smooth,  ^xvd  in  the  middle  portion,  mixed. 

The  involuntary  variety  continues  throughout  the  remainder 
of  the  tract. 

The  FIBROUS  COAT  consists  of  fibro-elastic  tissues,  and  con- 
nects the  organ  with  the  surrounding  tissues.  It  sends  in 
bundles  between  the  muscle  bundles,  of  which  they  are  said 
to  form  the  perimysium. 

The  blood-vessels  pass  directly  to  the  submucosa,  where 
branches  are  formed,  and  sent  to  the  mucous  and  muscu- 
lar coats.     Here  they  form  longitudinal  plexuses. 

The  lymphatics  follow  the  same  general  course,  ^u^^^  Mu^  *M!!<Vi 

The  nerves  end  in  the  muscular  coat  and  beneath  the  epi-  g, 
thelial  cells.     Others  surround  the  glands. 

STOMACH. 

The  Stomach  is  the  first  part  of  the  tract  in  which  the 
food  rests  for  any  length  of  time,  and  in  which  active  diges- 
tion and  absorption  occur.  Although  very  large,  it  still  rep- 
resents a  tube,  and  has  the  four  coats  above  mentioned.  It 
is  divided  into  three  portions,  the  cardia,  fundus  and  py- 
loric END.  They  pass  into  one  another  insensibly,  and  the 
structure  of  the  first  two  parts  is  practically  the  same. 

The  MUCOUS  coat  presents  a  great  change  over  that  of 
the  esophagus,  showing  a  higher  degree  of  specialization. 
In  it  are  seen,  with  the  naked  eye,  a  number  of  minute 
depressions,  the  gastric  crypts,  or  pits,  from  which  the  gas- 
tric glands  extend  into  the  deeper  portions.  Between  or 
bounding  the  pits,  are  the  inter  glandular  projections.  Each 
gland  consists  of  mouth,  neck  and  fundus,  or  secretory  por- 
tion, and  is  lined  by  simple  epithelial  cells. 


Il8  ALIMENTARY    TRACT. 

The  cells  rest  upon  a  basement  membrane,  which,  in  turn, 
rests  upon  the  tunica  propria.  The  latter  forms  the  core  of 
the  interglandular  projections  that  form  the  boundaries  of 
the  pits.  Between  the  glands,  the  tunica  propria  consists  of 
narrow  bands  of  the  fibrous  tissue,  which  contains  a  great 
deal  of  diffuse  adenoid  tissue,  bundles  of  muscle  fibres  from 
the  muscularis  mucosae,  and  capillaries,  both  vascular  and 
lymphatic,  in  great  numbers.  In  places,  the  adenoid  tissue 
is  collected  into  solitary  follicles  that  are  lens-shaped,  and 
are  called  the  lenticular  follicles,  or  glands.  These  are 
numerous  in  the  pyloric  end.  The  mucosa  is  bounded  ex- 
ternally by  the  muscularis  mucosae,  which  consists  of  two 
layers  of  smooth  muscle  fibres,  arranged  as  inner  circulaf 
and  outer  longitudinal  bands. 

In  the  cardiac  and  fundal  portions,  the  secretory  portions 
of  the  glands  are  chiefly  of  the  simple  tubular  variety.  The 
mouth  is  short,  with  the  neck  and  fundus~6Fabout  the  same 
length.  In  the  neck  and  fundus,  are  found  two  varieties  of 
low  columnar  cells,  the  chief,  peptic,  or  adelomorphous  cells, 
and  the  large  delomorphous,  acid,  oxyntic,  or  acid  cells. 

The  peptic  cells  are  low  columnar  elements,  and  are  found 
more  numerous  in  the  fundus  than  in  the  neck.  The  nucleus 
is  usually  circular  or  oval,  and  takes  the  stain  very  well. 
These  cells,  in  the  glands,  have  an  affinity  for  the  hematoxy- 
lin, and  appear  bluish  when  characteristically  stained.  They 
also  line  the  motith  and  pits,  and  cover  the  interglandular 
projections.  In  these  places,  the  cells  become  very  much 
longer,  and  take  the  stain  but  faintly.  They  form  a  broad 
band  of  palely  stained  protoplasm,  in  which  the  darkly 
stained  nuclei  have  a  basal  location,  forming  a  row  of 
closely-placed  bodies.  The  lateral  boundaries  are  not  dis- 
tinct, but  the  nuclei  indicate  the  breadth  of  the  cell.  Alto- 
gether,  they  give  a   feather-like   appearance  to  the   inter- 


STOMACH. 


119 


glandular  projections.    Besides  the  peptic  cells,  a  few  goblet 
cells  are  found  in  the  latter  region. 

The  acid  cells  are  readily  distinguished  from  the  others 
by  their  size,  shape,  and  affinity  for  acid  stains.     They  are 


iS-'f 


rn 
n 
o 


:^ 


.1^ 

r 


Fig.  48. — Cross-section  Segment  of  Stomach. 
A.  Cardiac  Region — a.  mucous  coat ;  ft.  submucous  coat ;  c.  muscular  coat ; 
d.  fibrous  coat ;  e.  epithelium  ;  /.  interglandular  projection  ;  [).  base- 
ment membrane  ;  U.  gastric  pit ;  1  neck  of  gland  ;  k.  acid  cell ;  I.  tunica 
propria;  m,  n.  layers  of  muscularis  mucosae;  0.  submucosa ;  p.  cir- 
cular layer  of  muscular  coat ;  q.  longitudinal  layer  of  muscular  coat ; 
r.  oblique  layer  of  muscular  coat ;  s.  white  fibrous  tissue  layer  con- 
taining the  nerve  plexus  of  Auerbach.  B.  Gland  of  Cardiac  Region 
of  Stomach — a.  gastric  pit ;  &.  columnar  epithelium  ;  c.  goblet  cell  ; 
d.  basement  membrane ;  e.  tunica  propria  of  interglandular  projec- 
tion ;  f.  neck  of  gland  ;  g.  acid  cell ;  h.  peptic  cell. 

very  large,  oval,  or  triangular  elements,  most  numerous  in 
the  neckSj  but  also  scattered  in  the  fundus.  They  are  found 
along  the  wall  of  the  tubule,  and  usually  beneath  the  peptic 


I20  ALIMENTARY    TRACT. 

cell,  hence  the  term  parietal,  or  zvall,  cell.  The  nucleus  is 
quite  large,  and  centrally  located,  and  the  protoplasm  con- 
tains minute  canals.  The  affinity  for  acid  stains  is  pro- 
nounced. With  eosin,  they  are  distinctly  red,  while  with 
acid  fuchsin  they  are  colored  a  very  much  deeper  red.  These 
cells  are  supposed  to  form  the  hydrochloric  acid. 

In  the  first  portion  of  the  fundus,,  the  glands  are  chiefly 
of  the  simple  tubular  variety.  As  the  pyloric  end  is-  ap- 
proached, the  branched  tubulars  begin  to  increase,  so  that 
they  form  the  predominating  variety  in  this  end.  There  is 
also  a  marked  change  in  the  lining  cells.  The  acid  cells  be- 
come rapidly  fewer  in  number,  and,  in  the  pyloric  end,  are 
but  seldom  seen.  One  can,  therefore,  be  safe  in  saying  that 
a   section   containing  a  number   of  acid   cells   is   from   the 

FUNDUS^   or   CARDIA. 

In  the  PYLORIC  end,  the  glands  are  different.  The  mouth 
becomes  longer  and  wider,  and  the  fundus  and  neck  com- 
paratively shorter.  THe  lumen  of  the  fundus  is  broader,  and 
the  cells  are  only  of  the  peptic  variety.  These  cells  are  usual- 
ly longer  and  broaSeTthdin  those  in  the  cardiac  glands,  and 
have  distinct  cell  boundaries  and  prominent  basal  nuclei.  The 
protoplasm,  however,  does  not  respond  well  to  the  stain,  but 
is  always  pale.  As  the  pyloric o-duodenal  junction  is  reached, 
the  glands  become  shorter  and  less  numerous,  and  some 
may  even  extend  into  the  submucosa.  The  inter  glandular 
projections  become  longer,  and  resemble,  somewhat,  the 
VILLI  of  the  small  intestine. 

The  MUCOSA  and  submucosa  are  thrown  into  large  folds, 
the  rugae.  These  folds  and  glands  increase  greatly  the  ab- 
sorptive and  secretory  surfaces. 

The  submucous  coat  consists  of  loosely  arranged  white 
fibrous  tissue,  in  which  the  larger  blood-vessels  are  seen. 

The  muscular  coat  is  composed  of  smooth  muscle  ar- 
ranged into  three  layers.     Of  these,  the  inner  is  oblique; 


STOMACH. 


121 


the  middle,  circular,  and  the  outer,  longitudinal.  At  both 
openings  of  the  stomach,  the  circular  fibres  are  more  numer- 
ous, and  form  sphincters:  Of  these  the  sphincter  pylori  is 
the  more  prominent. 

The  FIBROUS,  SEROUS  or  PERITONEAL  COAT  is  composcd  of 
a  thin  layer  of  white  fibrous  tissue,  covered  by  a  reflection  of 
the  peritoneum. 


J/' 


Fig.  49. — i.uMari  diaal  Hkction  of  Segment  of  Pyloric  Region  of 
Stomach. 

a.  Mucous  coat ;  h.  submucous  coat ;  c.  muscular  coat ;  d.  fibrous  coat ; 
e.  interglandular  projection  ;  f.  epithelium ;  .(/.  basement  membrane ; 
h.  gastric  pit ;  i.  pyloric  glands  ;  k.  tunica  propria ;  I.  muscularis  mu- 
cosae ;  m.  bloodvessel  ;  n.  connective  tissue  in  muscular  coat ;  o.  inner 
circular  layer  of  muscle  ;  p.  outer  longitudinal  layer  of  muscle. 


Throughout  the  alimentary  tract,  the  chief  vessels  are 
found  in  the  submucosa,  and  from  this  coat,  the  branches 
are  sent  to  the  mucosa  and  muscularis.  In  the  stomach, 
the  vascular  and  lymphatic  capiUariej  are  very  numerous 
in  the  tunica  propria.  The  lymphatics  empty  into  larger 
vessels  in  the  submucosa,  in  which  the  veins,  also,  are 
formed. 


122  ALIMENTARY    TRACT. 

The  NERVES  are  chiefly  sympathetic,  and  are  arranged  in 
two  plexuses,  one  in  the  submucosa,  and  the  other  in  the 
muscular  coat.     (See  Intestine,  p.  130). 

SMALL  INTESTINE. 

The  Intestinal  Tract  consists  of  two  main  portions,  the 
Small  and  Large  Intestines.  These  each  have  their  sub- 
divisions, which  usually  differ  from  one  another. 

The  Small  Intestine  is  divided  into  duodenum,  jejunum 
and  ILEUM.  They  all  have  the  same  general  structure. 
This  will  first  be  described,  and  then  the  differences  studied. 

There  are  four  coats,  mucosa,  submucosa,  muscularis  and 
Uhrosa,  or  serosa. 

The  MUCOSA  has  four  layers,  epithelium,  basement  mem- 
brane, tunica  propria  and  muscularis  mucosae.  It  contains 
a  large  number  of  simple  tubular  glands,  the  crypts  of  Lieber- 
kuehn,  or  intestinal  crypts.  Above  the  level  of  the  glands, 
the  mucosa  is  thrown  into  an  immicnse  number  of  small, 
finger-like  projections,  the  villi. 

The  epithelium  is  chiefly  of  the  simple  columnar  variety, 
with  varying  numbers  of  goblet  cells.  Those  within  the 
gland  are  nearly  conical  in  shape,  and  stain  darkly.  The 
protoplasm  is  granular,  and  the  nucleus  basal.  Upon  the 
villi,  the  cells  are  columnar,  and  the  protoplasm  granular  and 
reticular,  while  the  exposed  margin  is  differentiated  into  a 
cuticular  border.  Some  hold  that  the  cells  in  the  glands  se- 
crete a  fluid  used  in  digestion;  others  consider  them  goblet 
cells  in  different  stages. 

The  goblet  cells  are  distinctly  columnar  elements,  in  which 
the  position  of  the  nucleus  varies  with  the  state  of  secretion. 
They  form  the  mucin.  The  protoplasm  is  granular  and  retic- 
ular, and,  when  mucin  is  forming,  shows  small  clear  areas ; 
these  fuse  to  form  a  single  large  drop  of  mucin  that  forces 


SMALL    INTESTINE.  I23 

the  protoplasm  and  nucleus  to  the  basal  portion  of  the  cell. 
The  sides  are  curved,  producing  the  goblet  form.  When 
the  cuticular  border  ruptures,  and  the  mucin  is  discharged, 
the  cell  becomes  slender  and  irregular.  These  celts  are 
found  mostly  upon  the  villi,  and  become  more  numerous  as 
the  large  intestine  is  approached. 

The  tunica  propria  consists  of  delicate  white  fibrous  tissue 

657 


^^^;^f^'ik. 


mm^'^^'      .  #v— ^ 


¥?^ 


I 


Fig.  50.- — Ckos.s-section  of  Duodenum. 
1.   Mucous  coat ;   2.   submucous   coat ;   3.   muscular   coat ;   4.   fibrous  coat ; 
5,  6.  villi  ;  7.  epithelium  of  villus  ;  8.  muscularis  mucosae ;  9.  glands 
of  Brunner. 


that  forms  the  core  of  the  villi.  It  contains  diffuse  adenoid 
tissue  and  capillary  vessels,  both  lymphatic  and  vascular. 

The  muscularis  mucosae  consists  of  two  layers  of  smooth 
muscle  fibres  arranged  circularly  and  longitudinally.  From 
it,  bundles  are  sent  up  into  the  villi. 

A  VILLUS  is  a  finger-like  projection  of  the  tunica  propria, 
covered  by  a  basement  membrane  and  epithelial  cells  of  the 
simple  columnar  and  goblet  varieties.     The  tunica  propria 


124 


ALIMENTARY    TRACT. 


forms  the  core, -and  contains  considerable  diffuse  adenoid 
tissue,  a  large  number  of  capillary  bloodvessels,  muscle  fibres 
and  a  space  in  the  center  called  the  lacteal.    It  is  by  the  villi 


Fig.   51. — Longitudinal  Section  op  the  Upper  Part  of  a  Villus 
OB^  A  Dog. 
a.  Epithelium  ;  h.  tunica  propria ;  c.  capillary  ;  d.  cuticular  border  of  the 
epithelium ;    e.   nucleus  of   wandering  leukocyte ;   f.   section  of  goblet 
cell ;  g.  mucoid  area  of  goblet  cell ;  h.  lacteal ;  i.  smooth  muscle  fibre 
{Stohr's  Histology). 


that  nature  increases  the  absorptive  surface  enormously 
The  lacteal  is  the  starting  point  of  the  lymphatic  system  of 
the  intestine. 


SMALL    INTESTINE.  I25 

The  adenoid  tissue  is  often  collected  into  solitary  follicles 
that  are  usually  present  in  the  mucosa,  and  in  such  areas  the 
glands  and  villi  are  generally  absent. 


I 


Fig.  52. — Cross-section  of  Ileum. 

a.   Villus;     6.   epithelium;    c.   tunica  propria   of  villi;    d.   gland   of  Lieber- 

kuehn ;   e.  tunica  propria  ;  f,  f.  muscularis  mucosae  ;  g.  blood-vessel ; 

h.  submucosa ;  i.  circular  muscle  layer  ;  k.  longitudinal  muscle  layer ; 

I.  peritoneal  layer ;  m.  fibrous  coat ;  n.  tollicles  of  the  Peyer's  patch. 

The  mucosa  and  submucosa  are  thrown  into  circular 
folds.  These  are  the  valvulae  connivcfites,  or  folds  of  Kerh 
ring.    They  are  seen  upon  longitudinal  section  of  the  bowel 


126  ALIMENTARY    TRACT. 

The  SUBMUCOSA  consists  of  loose  bundles  of  white  fibrous 
tissue,  and  here  are  to  be  found  the  main  vascular  and  lym- 
phatic trunks.  It  enters  into  the  formation  of  the  valvulae 
conniventes,  and  contains  the  glands  of  Briinner  of  the  duo- 
denum, and  the  Peyer's  patches  of  the  ileum. 

The  MUSCULAR  COAT  is  composed  of  inner  circular  and 
outer  longitudinal  layers.  These  are  well  developed  in  the 
duodenum,  but  become  thinner  as  the  colon  is  approached. 

The  ahrous  coat  is  thin,  and  nearly  the  whole  of  the  intes- 
tine is  covered  by  peritoneum,  forming  a  serous  coat. 

The  JEJUNUM  contains  no  special  structures. 

The  ILEUM  is  characterized  by  agminated  follicles,  or 
Peyer's  patches.  These  are  collections  of  solitary  follicles 
(lo  to  60),  generally  found  in  both  the  mucosa  and  submu- 
cosa.     Each  follicle  usually  shows  a  germinal  center. 

The  DUODENUM  is  characterized  by  the  presence  of  a 
large  number  of  tuhulo-alveolar  glands  in  its  submucosa. 
The  excretory  ducts  open  at  the  bases  of  the  villi,  and  pour 
their  secretion  into  the  lumen  of  the  intestine.  These  are 
the  glands  of  Brunner,  and  they  give  rise  to  the  succus 
entericus. 

LARGE  INTESTINE. 

This-  consists  of  Cecum,  Colon,  Rectum  and  Appendix. 
The  structure  of  all  is  practically  the  same. 

The  MUCOSA  contains  simple  tubular  glands,  crypts  of 
Lieberkuehn,  which  are  usually  short,  and  broader  than 
those  of  the  small  intestine.  The  cells  lining  these  are  goblet 
cells.  The  tunica  propria  contains  a  great  deal  of  dififuse 
adenoid  tissue  that  is  often  collected  into  solitary  follicles 
that  show  germinal  centers.  Valvulae  conniventes  and  villi 
are  absent. 

The  outer  three  coats  are  like  those  of  the  small  intestine, 
except  for  difference  in  the  muscular  coat.     The  longitu- 


LARGE    INTESTINE. 


127 


dinal  fibres  are  usually  arranged  into  three  bands,  thejaeniae^ 
coli.jwhich  are  about  one-sixth  shorter  than  the  bowel.  These 
act  as  a  purse  string  to  the  intestine,  and  cause  it  to  be 
thrown  into  a  number  of  sacculations.     If  ^the  bands  be  re- 
moved, the  sacculations  disappear. 

The  Rectum  has  its  mucous  and  submucous  coats  formed 
into  folds  called  the  rectal  valves.    These  contain  a  continua- 


Fig.    53. — Cross-section    Segment   op   Colon. 

a.  Mucous  coat ;  6.  su'jmucous  coat ;  c.  muscular  coat ;  d.  fibrous  coat : 
e.  columnar  cell  ;  f.  goblet  cell  :  g.  basement  membrane :  h.  tunica 
propria  :  i.  inner  circular  layer  of  muscularis  mucosae ;  k.  outer  longi- 
tudinal layer  of  muscularis  mucosae  ;  I.  inner  circular  layer  of  muscu- 
lar coat ;  m.  outer  longitudinal  layer  of  muscular  coat. 


I 


tion  of  the  muscular  coat,  by  means  of  which  the  valves  may 
e  prdtuded  into  the  lumen.  At  the  lower  end,  the  anus, 
straiiHed  squamous  cells  replace  the  simple  columnar,  and 
this  marks  another  imico- cutaneous  junction  as  in  the  lips. 
I  The  Appendix  is  a  continuation  of  the  cecum.  It  has 
the    four    coats,    mucosa,    submucosa,    muscularis    and 

^FIBROSA,  or  SEROSA, 


128  ALIMENTARY    TRACT. 

The  MUCOSA  is  usually  irregular,  and  consists  of  simple 
columnar  epithelial  cells  that  rest  upon  a  basement  mem- 
brane; beneath  the  latter  lies  the  tunica  propria,  which  is 
bounded  by  the  miiscularis  mncosae. 

In  the  MUCOSA  are  a  large  number  of  tube-like  depressions, 
the  glands  of  Lieberkuehn.  These  possess  an  equal  diameter 
throughout,  and  are  quite  regularly  distributed.  The  cells 
of  the  mucosa  are  the  simple  columnar  variety,  interspersed 
with  many  goblet  cells.  They  are  quite  distinct,  and  usually 
possess  a  basal  border.  The  cells  in  the  base  of  the  glands 
supply  the  parts  higher  up,  and  are  consequently  the  young- 
est. The  glands  are  about  25,000  (Kelly  and  Hurdon)  in 
number,  and  are  absent  where  the  solitary  follicles  are 
found. 

The  tunica  propria  consists  of  a  delicate  fibro-elastic 
stroma  containing  many  capillaries,  considerable  diffnse 
adenoid  tissue  and  solitary  follicles  (often  300  to  400  in  num- 
ber). The  solitary  follicles  contain  germinal  centers,  and 
may  extend  into  the  submucosa.  Immediately  over  them, 
the  glands  are  usually  absent. 

The  mnscnlaris  mucosa  is  not  always  present.  It  consists 
of  smooth  muscle  fibres  formiing  a  thin  band  separating  the 
mucosa  from  the  submucosa. 

The  SUBMUCOSA  consists  of  loose  white  fibrous  tissue,  and 
supports  the  larger  blood  vessels.  In  older  subjects,  it  be- 
comics  thicker  and  denser,  and  passes  into  the  tunica  propria. 

The  MUSCULAR  coat  is  usually  separable  into  two  distinct 
layers,  inner  circular  and  oiUer  longitudinal.  The  former  is 
the  more  prominent,  and  extends  to  the  blind  end,  where  the 
fibres  form  a  dome-like  collection  of  interlacing  fibres.  The 
longitudinal  fibres  are  less  prominent  than  the  circular.  Both 
layers  are  pierced,  at  intervals,  by  large  vessels.  Such  an 
opening,  of  which  one  especially  exists  at  the  blind  end,  is 
called  an  hiatus  (Kelly  and  Hurdon). 


APPENDIX. 


129 


The   SEROUS   coat   consists   of   white  fibrous   tissue,   sur- 
rounded by  the  peritoneum. 

The  lumen  tends  to  disappear  more  frequently  than  sup- 


FiG.  54, — Cross-section  of  Human  Appendix. 

a.  Liumen ;  &.  epithelium  ;  c.  basement  membrane ;  d.  glands ;  e.  tunica 
propria ;  f.  diffuse  adenoid  tissue  :  p.  muscularis  mucosae  ;  h.  solitary 
follicle:  i.  adipose  tissue;  k.  submucosa ;  I.  circular  muscle  fibres; 
m.   longitudinal   muscle  fibres ;  n.   fibrous  coat. 


posed ;  this  change  occurs  during  the  ages  ranging  from  20 
to  80.  The  older  the  individuals,  the  higher  the  percentage 
of  occlusions.     The  glands  are  gradually  destroyed  bv  the 


130  ALIMENTARY    TRACT. 

thickening  of  the  submucosa,  this  process  beginning  at  the 
Wind  extremity  and  proceeding  toward  the  bowel.  Occa- 
sionally, in  this  process  of  occlusion,  adipose  tissue  is  seen 
in  the  submucosa  in  quite  an  abundance. 

The  chief  blood-vessels  of  the  intestines  pass  from  between 
the  layers  of  the  mesentery  into  the  submucosa.  From  these 
trunks,  branches  are  sent  to  the  various  coats.  In  the  villi, 
dense  capillary  plexuses  are  formed  around  the  lacteals,  and, 
lower  down  in  the  mucosa,  around  the  gland.  The  blood  is 
returned  to  the  submucosa  through  venous  channels,  and 
these  unite  here  to  form  the  main  venous  trunks  that  leave 
the  intestine  to  pass  between  the  layers  of  the  mesentery. 

The  lymphatics  of  the  intestine  start  as  the  lacteals.  These 
pass  from  the  apices  of  the  villi  to  the  bases,  where  they 
open  into  a  set  of  vessels  near  the  muscularis  mucosae.  From 
this  plexus,  vessels  connect  with  another  network  in  the  sub- 
mucosa. The  latter  receives  lymph  through  other  vessels 
that  encircle  the  solitary  follicles  and  patches.  From  this 
suhmiicoiis  plexus,  vessels  pierce  the  muscular  coat  to  pass 
between  the  layers  of  the  mesentery,  receiving,  at  the  same 
time,  branches  from  the  muscularis  itself.  Ultimately,  these 
channels  empty  into  the  ^^ceptqculum  chyli,  or  cistern  of 
Peqiie\t.  The  chyle  vessels,  or  lacteals,  are  usually  guarded, 
at  the  base,  by  a  valve  that  prevents  regurgitation,  and  aids 
in  producing  a  vacuum  in  the  lacteals,  thus  aiding  absorp- 
tion. 

The  nerves  are  chiefly  sympathetic  and,  as  in  the  stomach, 
two  plexuses  are  formed.  The  plexus  of  Meissner  lies  in  the 
submucosa,  and  that  of  Auerbach  in  the  muscular  coat,  be- 
tween the  circular  and  longitudinal  layers.  Where  the 
plexus  fibres  join,  little  collections  of  multipolar  cells,  called 
ganglia,  are  formed.  The  plexus  of  Meissner  seems  to  be 
a  derivative  of  the  plexus  of  Auerbach.  The  mucosa  is  sup- 
plied by  fibres  from  the  former. 


CELLS    LINING    ALIMENTARY    TRACT. 


131 


The  cells  lining  the  various  portions  of  the  Alimentary 
Tract  are  as  follows : 

Lips Stratified  squamous. 

Mouth Stratified  squamous. 

Tongue.  .■ Stratified  squamous. 

Pharynx Stratified  squamous. 

Esophagus Stratified  squamous. 

Acid  cells. 


Cardiac  end. 


Stomach   ■< 


Pyloric  end. 


Small  intestine. 


Peptic  cells. 
Tall  columnar. 
Goblet  cells  (a  few). 
"    Peptic  cells. 
Tall  columnar. 
Goblet  cells. 

f  Simple  columnar. 
I  Goblet  cells. 

T  f  Goblet  cells. 

Large  intestine <^ 

)  Simple  columnar. 

Anus Stratified  squamous. 

The  differences  between  the  Small  and  Large  Intestines 
are  as  follows : 

Small.  Large. 

Long  and  narrow.     Broad. 
Chiefly  glandular.  Chiefly  goblet. 
Present.  Absent. 

Present.  Absent. 

Present.  Absent. 

Present.  Absent. 

Present. 
Present. 


Glands. 

Cells. 

Villi. 

Valvulae. 

Brunner's  glands. 

Peyer's  patches. 

Longitudinal  bands.Absent. 

Sacculations.  Absent. 


ti^i^/v^^'#*i/^-j*^ -^ 


mJ 


CHAPTER  X. 


THE  DIGESTIVE  GLANDS. 

The  Digestive  Glands  are  the  Liver,  and  Salivary 
Glands,  the  Parotid,  Pancreas,  Sublingual  and  Submaxil- 
lary. 

LIVER. 

The  Liver,  the  largest  gland  in  the  body,  is  compound 
tubular  in  structure.  It  is  surrounded  by  a  sheath  of  white 
fibrous  tissue,  the  capsule  of  Glisson,  which  is  covered  by 
peritoneum.  On  the  under  surface  of  the  organ,  the  capsule 
follows  the  blood-vessels  at  the  transverse  fissure  into  the 
gland,  and  forms  the  interlobular  connective  tissue.  Folds 
and  bands  form  the  various  ligaments,  suspensory,  coronary 
and  two  later aL  The  round  ligament  is  formed  by  the  per- 
sistent, closed  umbilical  vein. 

The  Liver  is  divided  into  lobes  and  lobules,  of  which  the 
latter  represent  the  units.  A  description  of  a  lobule  will  suf- 
fice for  that  of  the  whole  liver. 

Each  Lobule  consists  of  a  collection  of  radiating  chains 
of  hepatic  cells,  the  tubules,  that  start  from  the  central, 
or  INTRALOBULAR  VEIN.  These  chains  are  separated  from 
one  another  by  reliculum,  which  supports  the  cells  and  the 
INTRALOBULAR  CAPILLARIES.  Each  chaiu  consists  of  two  or 
three  cells  side  by  side,  enclosing  a  smiall  capillary  space 
called  the  bile  capillary.  Peripherally,  the  lobules  are  not 
separated  from  one  another  by  connective  tissue,  except  in 
the  pig  and  camel.  In  these  animals,  the  lobules  are  sharply 
outlined  by  bands  of  connective  tissue.  This  occurs  some- 
what imperfectly  in  the  human  liver  under  pathologic  condi- 
tions (chronic  interstitial  hepatitis). 

132 


LIVER. 


133 


The  HEPATIC  CELLS  are  large,  mononuclear  masses  of  pro- 
toplasm, although  occasionally  two  nuclei  may  be  present. 


Fig.   55. — Liver   of   Pig. 
a.  Interlobular  connective  tissue  containing  a  portal  system  consisting  of 
r  b.   Interlobular    branch    of   hepatic   artery. 
■<  c.   Interlobular  branch  of  portal  vein. 
Id.   Interlobular  branch  of  bile  duct. 
e.   chains  of  hepatic  cells ;   f.   central   vein  ;   g.   chain  of  cells  highly 
magnified. 

The  protoplasm  is  granular,  and  may  contain  droplets  of  fat, 
glycogen  and  even  pigment  granules.  The  cells  are  traversed 


T34  THE   DIGESTIVE    GLANDS. 

by  minute  canals,  secretory  capillaries,  that  open  into  the 
bile  capillaries  lying  between  the  cells.  These  cells  are  ar- 
ranged in  irregular  chains  that  consist  of  two  or  three  cells, 
in  cross-section,  and  extend  from  the  central  vein  to  the  peri- 
phery of  the  lobule.    Such  are  the  hepatic  tubules. 

The  bile  capillaries,  that  lie  between  the  cells,  are  merely 
notches  in  the  apposed  cells.  They  start  blindly  at  the  cen- 
tral vein,  pass  to  the  periphery,  and  empty  into  interlobu- 
lar vessels  that  possess  a  low  columnar  epithelial  lining  sup- 
ported by  basement  membrane  and  tunica  propria.  These 
unite  to  form  larger  vessels  that  are  lined  by  tall  columnar 
cells.  The  interlobular  ducts  that  lie  between  the  lobules 
are  lined  by  the  same,  and  possess,  in  addition,  some  muscu- 
lar tissue. 

The  interlobular  connective  tissue  is  seen  in  abun- 
dance, at  times,  at  the  junction  of  several  lobules.  In  such 
areas  will  be  found  branches  of  the  hepatic  artery  and  vein, 
portal  vein  and  bile  duct.  These  vessels,  with  the  connective 
tissue,  form  a  portal  system,  or  canal. 

The  CIRCULATION  of  the  liver  is  more  peculiar  and  inter- 
esting than  that  of  any  other  organ  in  the  body.  Two  systems 
bring  the  blood,  yet  it  leaves  through  one.  In  other  organs, 
the  vessel  that  supplies  the  functionating  tissue  is  an  artery, 
but  here  it  is  a  vein,  the  portal  vein. 

The  portal  vein  is  made  up  of  the  superior  ai^d  inferior 
mesenteries,  coronary\siomdic\\)  and  splenic  veins.  It  enters 
at  the  transverse  Ussure  of  the  liver,  and  forms  two  main 
branches,  right  and  left,  one  for  each  main  lobe.  These 
rapidly  form  interlobular  branches  that  give  rise  to  the 
intralobular  capillaries,  found  in  the  lobules,  where  they 
converge  at  the  center  and  empty  into  the  central,  or  intra- 
lobular VEIN. 


PORTAL    CIRCULATION.  1 35 

The  circulation  of  the  Hver  might  be  outHned  as  follows : 
Portal  vein. 

f 

Lobar  branches. 

I 


Interlobar  branches. 

f 

Interlobular  veins. 


Hepatic  artery. 

I 

Lobar  branches. 

I 

Interlobar  branches. 

f 

Interlobular  arteries. 
Interlobular  capillaries. 


Intralobular  capillaries 


\ 

Central  vein. 

! 

Sublobular  vein. 

f 

Interlobular  vein. 

I 

Interlobar  branches. 

f 

Hepatic  veins. 

The  hepatic  artery  enters  the  transverse  fissure,  and 
forms  lobar  and  interlobular  branches.  The  latter  rapidly 
form  capillaries  that  lie  in  the  interlobular  connective  tissti-e 
and  nourish  it,  and  the  vessels  found  here.     These  are  the 


136  THE   DIGESTIVE    GLANDS. 

INTERLOBULAR  CAPILLARIES,  some  of  whicli  enter  the  outer 
third  of  the  lobule  and  empty  into  the  portal  vein  capillaries. 
The  remainder  of  the  hepatic  artery  capillaries  empty  into 
the  interlobular  branch  of  the  portal  vein,  or  form  small 
venules  that  ultimately  empty  into  these. 

The  blood  that  has  entered  the  central  vein,  from  the 
portal  vein  and  the  hepatic  artery,  passes  into  the  sublobu- 
LAR  veins,  which  are  formed  by  a  union  of  the  centrals,  and 
then  into  the  interlobular  branches  of  the  hepatic  veins. 
The  interlobulars  are  formed  by  a  union  of  the  sublobu- 
lars,  and  these,  in  turn,  unite  to  form  the  hepatic  veins 
that  empty  the  blood  into  the  inferior  vena  cava.  As  the 
portal  vein  blood  comes  into  intimate  relation  with  the 
hepatic  cells,  the  latter  remove  the  products  required  for 
nutrition,  also  the  excess  of  glucose,  which  is  converted  into 
liver  sugar,  or  glycogen,  and,  in  addition,  take  out  the  con- 
stituents of  the  bile. 

I'he  lymphatics  follow  the  general  course  of  the  blood- 
vessels. The  blood-vessels  are  surrounded  by  lymph  spaces 
that  communicate  with  the  capillaries  and  with  similar  spaces 
in  the  periphery  of  the  lobule,  and  in  the  interlobular  con- 
nective tissue. 

The  sympathetic  nerves  form  the  chief  source  of  enerva- 
tion of  the  liver.  They  lie  in  the  interlobular  connective 
tissue  as  plexuses,  and  from  these  some  fibres  pass  to  the  bile 
ducts,  and  others  penetrate  the  lobules  to  pass  beneath  the 
cells. 

The  Excretory  Apparatus  consists  of  the  Gall-bladder, 
Hepatic,  Cystic  and  Common  Ducts.  They  all  possess 
three  coats,  mucous,  muscular  and  fibrous. 

In  the  Gall-bladder,  the  mucous  coat  consists  of  simple 
columnar  cells,  basement  membrane  and  tunica  propria;  the 
latter  is  thrown  into  folds,  in  which  the  muscular  coat  also 


SALIVARY  GLANDS.  1 37 

is  included.  In  this  layer,  a  few  mucous  glands  may  be 
found. 

The  MUSCULAR  coat  consists  of  a  mixture  of  smooth  muscle 
and  white  fibrous  tissue,  the  latter  predominating  near  the 
mucous  coat.  In  the  fibrous  tissue  are  found  the  chief  ves- 
sels that  supply  the  other  coats  with  branches. 

The  fibrous  coat  consists  of  white  fibrous  tissue,  covered 
by  the  peritoneum. 

The  lymphatics  are  connected  to  those  of  the  liver  by  the 
subserous  plexus,  into  which  the  vessels  from  the  muscular 
coat  empty. 

The  NERVES  are  sympathetic  and  cerebrospinal,  the  former 
passing  to  the  blood-vessels  and  muscles,  and  the  latter  end- 
ing in  the  mucosa,  near  large  arteries. 

The  Ducts  have  somewhat  the  same  structure,  containing 
a  few  mucous  glands  in  the  mucosa.  The  muscle  fibres  are 
quite  distinct.  They  are  arranged  as  circular,  longitudinal 
and  oblique  layers.  The  circular  fibres  of  the  common  duct 
form  a  sphincter  at  its  entrance  into  the  duodenum. 

SALIVARY  GLANDS. 

The  Salivary  Glands  are  the  Parotid,  Pancreas,  Sub- 
lingual and  Submaxillary  glands.  In  addition,  there  are 
a  large  number  of  small  unnamed  glands  in  the  lips,  mouth, 
tongue,  pharynx  and*  esophagus. 

According  to  secretion,  they  are  divided  into  mucous, 
serous  and  mixed. 

The*MUCOUS  glands  are  distinguished  by  their  large  secre- 
tory units  that  stain  lightly.  These  are  the  acini,  alveoli  or 
tubules,  and  they  give  rise  to  a  thick  viscid  secretion.  Such 
glands  are  the  small  glands  of  the  mouth,  pharynx  and 
esophagus.    The  Sublingual  is  almost  a  pure  mucous  gland. 


138  THE   DIGESTIVE    GLANDS. 

Serous  glands  are  those  in  which  the  acini  stain  darkly, 
owing  to  the  presence  of  secretory  granules  in  the  proto- 
plasm, which  retain  the  stain.  These  glands  secrete  a  thin 
albuminous  fluid.    Such  are  the  Parotid  and  Pancreas. 

The  mixed  glands  are  those  that  stain  both  lightly  and 
darkly,  and  secrete  a  mixed  fluid,  as  the  Submaxillary  and 
Sublingual. 

As  all  of  these  glands  have  the  same  general  structure, 
this  will  be  first  considered,  and  the  special  points  then  noted. 

Each  is  surrounded  by  a  capsule  of  white  fibrous  tissue 
that  limits  it  from  the  surrounding  organs  or  tissues.  The 
CAPSULE  sends  in  prolongations  that  divide  the  gland  into 
LOBES  and  lobules.  The  lobules,  or  structural  units, 
consist  of  the  functionating  ^mits  that  are  composed  of  a 
single  layer  of  glandular  epithelial  cells,  supported  by  a 
basefnent  membrane.  External  to  the  basement  membrane, 
is  the  interstitial,  or  intertubular,  connective  tissue,  which 
is  composed  of  reticulum,  and  in  which  the  blood-vessels, 
nerves  and  lymphatics  are  found. 

The  SECRETORY  UNITS  lead  into  minute  intermediate,  or 
intercalated,  TUBULES  that  unite  to  form  intralobular 
DUCTS,  which  pass  into  the  interlobular  connective  tissue. 
Here  they  unite  to  form  the  interlobular  ducts;  these,  by 
union,  form  the  lobars,  and  then  the  single  excretory  duct. 
The  intermediate  tubules  are  lined  by  simple  squamous, 
or  lozv  columnar  cells,  supported  by  basement  membrane  and 
interstitial  tissue;  the  intralobular  branches  contain  simple 
columnars,  the  interlobulars  and  interlobars  are  lined 
by  simple  pseudo-stratiUed  columnars,  and  the  excretory 
duct  usually  by  straiiUed  columnars.  In  the  latter,  the  mus- 
cular coat  is  distinct. 

The  blood-vessels  follow  the  divisions  of  the  ducts,  and 
form  plexuses  of  capillaries  around  the  units,  and  in  close 
proximity  to  the  epithelium. 


PAROTID  AND    PANCREAS.  1 39 

The  NERVES  pass  down  in  the  same  manner,  and,  after 
penetrating  the  basement  membrane,  end  around  the  cells. 

The  Parotid  Gland,  a  compound  alveolar  gland,  consists 
of  small,  serous  acini,  lined  by  cells  adapted  to  fit  these  alve- 
oli. The  actively  secreting  cell  has  a  very  granular  proto- 
plasm, but  that  of  the  resting  cell  contains  but  few  granules. 
As  the  granules  increase,  the  protoplasm  decreases,  until 
expulsion  of  the  secretion,  and  then  the  protoplasm  again 
increases.    Secretory  capillaries  exist  between  the  cells. 

This  gland  is  not  so  definitely  limited  as  the  others,  and, 
as  a  consequence,  adipose  tissue  may  be  seen  in  the  inter- 
lobular connective  tissue,  and  the  ductular  system  is  said  to 
be  more  highly  differentiated  than  in  any  other. 

The  duct  of  Stenon,  or  Siensen,  is  the  excretory  duct. 

The  Pancreas,  the  other  serous  gland,  is  also  compound 
alveolar  in  structure.  It  is  also  called  the  abdominal  salivary 
gland.  The  acini  and  tubules  are  usually  distinct  and- 
sharply  outlined.  In  these,  occasionally,  a  small  fiat  cell  is 
seen  occupying  a  central  position ;  this  is  a  centro-acinar  cell, 
and  is  supposed  to  be  one  of  the  cells  lining  the  intermediate 
tubules  that  extends  into  the  acini.  In  addition  to  the  acini, 
certain  peculiar  collections  of  lightly-staining  cells  are  seen. 
These  are  oval  or  circular  in  outline,  and  surrounded  by  a 
capsule  of  white  fibrous  tissue.  The  cells  are  divided  into 
groups,  each  of  which  seems  to  be  environed  by  a  collection 
of  capillaries.  These  are  the  areas,  or  islands  of  Langer- 
hans,  and  possess  no  outlet  for  the  secretion  they  are  sup- 
posed to  form,  which  is,  therefore,  supposed  to  be  absorbed 
by  the  blood-vessels.     Such  is  an  internal  secretion. 

The  EXCRETORY  DUCT,  the  DUCT  OF  WiRSUNG,  is  lined  by 
simple  columnar  cells. 

The  Sublingual,  a  tuhulo-alveolar  gland,  according  to 
some,  is  purely  mucous,  and  differs  from  the  above  in  pos- 
sessing lightly-staining  cells  in  the  secretory  units.     These 


140. 


THE   DIGESTIVE   GLANDS. 


cells  are  large  and  clear  during  secretory  activity,  but  smaller 
and  cloudy  after  expulsion  of  the  contents.  The  nucleus  is 
usually  peripheral,  in  the  former  condition.  Besides  the 
above  cells,  there  are  certain  darkly-staining  cells  or  cell- 
groups,  at  the  periphery  of  the  tubules,  lying  between  the 
mucous  cells  and  the  basement  membrane.     These  are  cres- 


FiG.  56. — Section  of  Human  Panckeas  showing  Areas  op  Langeriians. 
a.  Interlobular  connective  tissue ;  b.  capillary  ;  c.  interlobular  duct ;  d.  in- 
tralobular duct ;  e.  cells  of  acini ;  f.  area  of  Langerhans. 

cent-shapedj  and  are,  therefore,  called  the  crescents  of  Gian- 
uzzi,  or  demilunes  of  Heidenhain.  According  to  Stohr,  they 
represent  stages  of  secretory  activity,  in  which  the  cells  have 
expelled  their  secretion.  Others  hold  them  to  be  separate 
SEROUS  cells,  and  that  accounts  for  their  dark  stain.  Secre- 
tory canals  are  said  to  exist  in  them,  and  this  would  seem  to 
point  to  a  serous  character. 


SUBMAXILLARY    GLAND. 


141 


The  DUCT  OF  Bartholin  is  the  main  excretory  duct.  The 
DUCT  OF  RiviNi  is  smaller. 

The  Submaxillary  is  a  mixe:d  gland  in  secretion,  and 
tubulo-aveolar  in  structure.  The  serous  and  mucous  units 
may  be  separated  into  lobules  or  lobes,  or  may  be  found  side 


^  #  -^  -^la^* 


'^€l^??1^:uTi^^Hr%^. 


I 


Fig.  57. — Section  op  Submaxillary  Gland  of  a  Fox. 
a.  Connective  tissue  :  h.  serous  acinus ;  c.  intralobular  ducts  ;  d.  lumen  of 
a    mucous    acinus ;    e.    mucous    cells ;    f.    demilune    of    Heidenhain ; 
g.   capillary. 

by  side  in  the  same  lobule.  The  serous  are  the  more  numer- 
ous in  man.  In  the  mucous  tubules,  demilunes  are  present. 
The  ducts  are  unusually  numerous,  forming  a  distinguish- 
ing feature  of  this  gland. 

The  excretory  duct  is  the  duct  of  Wharton. 


CHAPTER  XI. 


RESPIRATORY  SYSTEM. 

This  System  comprises  the  Nares,  upper  part  of  the 
Pharynx,  the  Larynx,  Trachea,  Bronchi  and  Lungs.  Al- 
though there  is  no  connection,  the  Thyroid  and  Parathy- 
roids are  included. 

The  Nares  are  lined  by  a  mucous  membrane,  which  differs 
according  to  the  function  of  the  part.  The  first  portion  is 
lined  by  stratiHed  squamous  cells,  continued  from  the  skin 
surface.  Here  are  found  some  large  hairs,  sweat  and  se- 
baceous glands.  Within  this  area,  the  true  respiratory 
portion  is  lined  by  stratified  ciliated  cells,  with  a  few  goblet 
cells  scattered  here  and  there.  Beneath  the  basement  mem- 
brane, the  tunica  propria  is  represented  by  a  delicate  fibrous 
tissue  containing  some  diffuse  lymphoid  tissue  and  some 
glands  of  the  mucous  and  serous  types.     Above  this  area, 

the  OLFACTORY  MUCOUS  MEMBRANE  IS  fouud. 

The  RESPIRATORY  portion  of  the  Pharynx,  continuous 
with  the  nares,  is  lined  by  stratified  ciliated  cells.  In  the 
tunica  propria,  glands  resembling  those  found  in  the  nares 
are  seen. 

LARYNX. 

The  Larynx  is  a  hollow,  cartilaginous  organ  connecting 
the  pharynx  with  the  trachea.  It  consists  of  epiglottis,  vo- 
cal CORDS  and  larynx  proper. 

The  EPIGLOTTIS  is  a  projecting  flap  that  protects  the  glot- 
tis during  deglutition.  It  is  covered  by  stratified  squamous 
cells  upon  both  sides,  and  these  are  continuous  at  the  edges, 
and  rest  upon  basement  membrane  and  papillated  tunica  pro- 
pria.   The  latter  is  composed  of  fibro-elastic  tissue,  and  con- 

142 


LARYNX.  143 

tains  diffuse  lymphoid  tissue,  and,  also,  some  glands,  near 
its  attachment.  In  the  epithelial  portion  of  the  posterior  sur- 
face, taste-buds  are  found.  Beneath  the  tunica  propria  is  the 
submucosal  which  consists  of  loose  white  fibrous  connective 
tissue.  In  it  is  found  a  plate  of  elastic  cartilage  that  gives 
the  stiffness,  and  also  the  elasticity,  to  this  organ. 

The  VOCAL  CORDS  comprise  the  true  and  the  false.  The 
FORMER  are  the  functionating  structures,  while  the  latter  are 
merely  heavy  folds  that  seem  to  resemble  the  former.  The 
TRUE  CORDS  alouc  are  of  importance. 

The  TRUE  VOCAL  CORDS  are  covered  by  stratified  squamous 
cells  that  are  supported  by  basement  membrane  and  tunica 
propria.  The  central  portion  consists  of  a  band  of  elastic 
tissue. 

Between  the  two  sets  of  cords,  there  is  a  space,  or  recess, 
upon  each  side,  called  the  ventricle  of  the  larynx. 

The  remainder  of  the  larynx  consists  of  mucous,  sub- 
mucous and  fibrous  coats. 

The  mucous  coat,  including  that  of  the  ventricles,  is  lined 
by  stratified  ciliated  epithelial  cells.  The  tunica  propria  con- 
tains a  great  deal  of  diffuse  lymphoid  tissue.  That  portion 
of  the  SUBMUCOSA  adjacent  to  the  tunica  propria,  possesses 
a  number  of  small  mucous  glands.  In  its  outer  portion,  the 
cartilage  masses  are  found. 

The  form  of  the  larynx  is  given  by  the  cartilages,  which 
are  chiefly  hyalin.  Those  of  Wrisberg  and  Santorini,  middle 
of  the  thyroid  and  the  apices  of  the  arytenoids  are  elastic 
cariilage. 

External  to  the  cartilage  is  the  fibrous  coat,  which  is  com- 
posed of  white  fibrous  tissue,  supports  the  other  coats, 
and  connects  the  larynx  to  the  surrounding  organs  or  tissues. 

The  blood-vessels,  nerves  and  lymphatics  are  numerous. 
The  circulatory  system  is  represented  by  several  networks  of 


144  RESPIRATORY    SYSTEM. 

large  vessels,  and  a  plexus  of  capillaries  in  the  tunica  pro- 
pria. 

The  lymphatics  closely  follow  the  bloodvessels. 

The  nerves  are  distributed  to  the  mucosa,  where  they  end 
near  and  within  the  epithelial  layer,  or  in  the  taste-buds. 

TRACHEA. 

The  Trachea  connects  the  larynx  with  the  lungs,  its  lower 
end  bifurcating  to  form  the  Bronchi.  It  has  three  coats, 
MUCOUS,  SUBMUCOUS  and  fibrous. 

The  MUCOUS  coat  is  a  continuation  of  that  of  the  larynx. 
It  is  composed  chiefly  of  stratified  ciliated  and  goblet  cells 
that  rest  upon  the  basement  membrane  and  tunica  propria. 
The  basement  membrane  is  usually  quite  prominent,  and  the 
tunica  propria  contains  considerable  diffuse  adenoid  tissue. 
It  consists  of  fibro-elastic  tissue,  in  which  the  fibres  have 
chiefly  a  longitudinal  direction.  That  portion  of  the  mucosa 
opposite  to  the  attachment  to  the  esophagus  is  lined,  at 
times,  by  stratified  squamous  cells,  and  is  usually  irregular. 

The  SUBMUCOSA  is  made  up  of  white  fibrous  tissue,  and 
supports  the  large  blood-vessels  and  a  large  number  of 
mucous  glands,  the  tracheal  glands.  These  lie  in  that  por- 
tion near  the  tunica  propria.  In  the  outer  part  are  found 
the  cartilage  rings. 

These  rings  are  C-shaped  masses  of  hyalin  cartilage,  with 
the  open  portion  at  the  attachment  of  the  organ  to  the  esopha- 
gus. These  masses  are  thickest  in  front,  and  taper  as  the 
ends  are  reached.  Although  the  cartilages  are  supposed  to 
consist  of  one  piece,  they  are  commonly  made  up  of  a  num- 
ber of  plates.  The  ends  of  the  C's  are  connected  by  traverse- 
ly  and  longitudinally  arranged  smooth  muscle  fibres,  which 
are  attached  to  the  inner  and  outer  perichondriums,  and  then 
bridge  the  spaces  between  the  ends  of  the  cartilage.     This 


TRACHEA. 


145 


strip  of  muscle  extends  the  length  of  the  trachea,  but  no  com- 
plete muscularis  is  present.  The  rings  are  sixteen  to  eighteen 
in  number,  and  are  separated  from  one  another  by  white 
fibrous  tissue. 


^  -•-■/•-• 


rrt 


Fig.  58. — Cross-section  of  Segment  of  the  Trachea. 
a.  Mucous  coat ;  6.  submucous  coat ;  c,  d.  fibrous  coat  containing  some  vol- 
untary striated  muscle,  I.  m;  e.  stratified  ciliated  epithelium;  f.  base- 
ment membrane  ;  g.  goblet  cells ;  h.  mucous  glands ;  i.  blood-vessel ; 
A;,  elastic  tissue  and  perichondrium ;  I.  longitudinal,  and  m,  cross- 
sections  of  voluntary  muscle  fibres. 

The  FIBROUS  coat  lies  outside  of  the  cartilage  rings,  and 
consists  of  white  fibrous  and  yellow  elastic  tissues. 

The    blood-vessels    and    lymphatics    have    their    larger 


146  RESPIRATORY    SYSTEM. 

branches  in  the  submucosa,  from  which  smaller  vessels  ex- 
tend to  the  other  coats,  and  form  capillaries. 

The  nerves  are  chiefly  sympathetic. 

The  Bronchi  have  the  same  general  structure  as  the 
trachea.  Usually,  the  C-shaped  ring  of  cartilage  is  replaced 
by  a  number  of  plates. 

LUNGS. 

The  Lungs  resemble  compound  racemose  glands,  the 
BRONCHI  corresponding  to  the  excretory  ducts. 

Each  Lung  is  invested  by  a  fibrous  sheath,  covered  almost 
entirely  by  serous  membrane,  the  visceral  layer  of  the 
PLEURA,  which  is  reflected  over  the  inside  of  the  pleural  cav- 
ity, as  the  parietal  layer  of  the  pleura.  Between  these  two 
layers  is  the  so-called  pleural  cavity,  but  as  the  lungs  fill  it  in 
the  living  condition,  it  does  not  exist  as  a  cavity.  In  it  is 
found  a  small  amount  of  lymph  that  lubricates  the  mem- 
branes. 

The  Pleurae  have  the  same  structure  as  other  serous 
membranes.  Each  consists  of  endothelial  cells  and  sub  endo- 
thelial connective  tissue  that  pass  from  the  lung  over  to  the 
body  wall.  The  sub  endothelial  tissue  is  continuous  with  the 
interlobular  connective  tissue  of  the  lung. 

Upon  the  internal  surface  of  the  lung  is  an  area,  in  which 
the  vessels  and  tubes  enter  and  leave  the  organ ;  this  is  the 
ROOT  of  the  lung,  and  here  no  serous  membrane  exists. 

The  LUNGS,  like  other  glands,  are  merely  systems  of  tub- 
ules that  branch  and  rebranch,  and  are  lined  by  difl^erent 
varieties  of  cells.  It  is  an  alveolo-tubular  gland,  and  al- 
though no  liquid  secretion  or  excretion  is  formed,  it  plays 
an  important  part  in  the  excretion  of  gases  and  organic 
matter  from  the  blood. 

The  Bronchi  divide  like  the  ducts  of  any  gland,  and,  ulti- 
mately, the  small  divisions  called  bronchioles  are  reached. 


LUNGS. 


147 


Each  BRONCHIOLE  forms  a  system  separate  and  closed  from 
its  neighbors.  The  bronchiole  (0.5  mm.  in  diameter)  di- 
vides into  the  respiratory  bronchioles  (0.3  to  0.4  mm.  in 
diameter)  ;  these,  in  turn,  give  rise  to  alveolar  ducts 
(0.2  mm.),  which  end  as  large  spaces^  the  alvei,  alveolar 


^X*«^i^''^fe":iT:D 


Fig.  59. — Section  of  Human  Lung. 

a.  Pleura ;  6.  alveolar  septum  ;  c.  alveus,  or  air  sac ;  d.  alveolus ;  e.  intra- 
lobular blood-vessel  :  f.  interlobular  blood-vessel ;  g.  interlobular  bron- 
chial tube ;  h.  cartilage  ;  i.  branch  of  pulmonary  artery  ;  A;,  gland. 

SACS  or  AIR  SACS  (0.3  by  5  mm.)  ;  along  the  walls  of  these 
divisions,  are  found  small  depressions,  the  alveoli^  or  sac- 
cules (0.05  to  0.1  mm.),  and  these  are  the  final  divisions. 

A  LOBULE,  or  STRUCTURAi.  UNIT,  consists  of  the  divisions 
of  a  bronchiole,  and  varies  from  0.3  cm.  to  3  cm.  in  diameter. 


148  RESPIRATORY    SYSTEM. 

It  is  surrounded  by  white  fibrous  tissue  containing  larger 
vessels  and  ducts,  which  are  called  interlobular,  and  are 
over  0.5  mm.  in  diameter,  and  contain  cartilage.  The  alvei, 
or  air  sacs,  are  separated  from  one  another  by  yellow  elastic 
tissue,  in  which  a  dense  capillary  plexus  is  found. 

As  the  BRONCHUS  divides  and  redivides,  the  tubules  con- 
tain less  and  less  cartilage.  The  first  important  change  is 
the  formation  of  a  complete  investment  of  cartilage,  com- 
posed of  a  number  of  plates.  As  this  occurs,  the  muscle 
tissue  begins  to  increase,  so  that  soon  a  distinct  layer  is  seen 
internal  to  the  cartilage.  The  lining  cells  are  stratified  cili- 
ated, but  the  whole  mucosa  becomes  irregular  and  corru- 
gated, due  to  the  formation  of  longitudinal  folds ;  as  the  di- 
visions become  smaller,  the  cartilage  diminishes.  The  glands 
disappear  when  a  diameter  of  i  mm.  is  reached.  The  carti- 
lage is  retained  until  a  diameter  of  0.5  mm.  is  attained 

Such  a  tubule  is  a  bronchiole.  It  is  lined  by  simple  cil- 
iated epithelial  and  goblet  cells,  supported  by  a  basement 
membrane  and  an  elastic  tunica  propria.  External  to  this, 
the  circular  muscle  fibres  are  quite  prominent,  and  as  a  re- 
sult, folds  are  formed.  The  fibrous  tissue  external  contains 
elastic  fibres,  as  vessels  and  nerves. 

The  RESPIRATORY  BRONCHIOLES  arise  by  a  division  of  the 
above  tubules.  They  are  lined  partially  by  simple  ciliated 
and  partially  by  nonciliated  cells.  The  former  are  of  the 
simple  variety,  and  few  in  number.  The  nonciliated  cells  at 
first  are  columnar,  but  quickly  give  way  to  low  cuboidal  and 
flattened  cells.  The  last  named  are  called  respiratory  epithel- 
ium. Along  the  walls  of  the  tubules,  little  depressions,  the 
alveoli,  are  seen,  and  here  the  respiratory  epithelium  is 
marked.  Muscle  fibres  are  found  beyond  the  tunica  propria, 
and  elastic  tissue  becomes  more  abundant. 

The  ALVEOLAR  DUCTS  contain  many  alveoli  lined  by  respir- 
atory epithelium,  which  consists  of  thin,  nonnucleated  plates 


LUNGS.  149 

of  various  sizes,  arranged  individually  or  in  groups.  The 
smaller  cells  are  derived  from  the  cuboidal  cells  by  inspira- 
tion, and  the  larger  are  formed  by  a  fusion  of  the  smaller 
ones.  The  walls  of  these  ducts  consist  of  tunica  propria, 
muscle  tissue  (which  disappears  when  the  end  of  this  tubule 
is  reached)  and  considerable  elastic  tissue  circularly  ar- 
ranged. 

The  alveolar  ducts  lead  into  the  alveus,  air  sac,  or  alve- 
olar SAC.  On  the  walls  of  this  part  are  the  small  depres- 
sions, the  ALVEOLI  or  saccules.  These  are  separated  from 
one  another  by  minute  partitions,  or  septa,  that  consist  of 
elastic  tissue  covered  by  simple  sqifdnwus  cells,  the  respira- 
tory epithelium.  The  alveoli  of  a  system  communicate  with 
one  another  by  means  of  small  channels,  or  pores.  At  the 
base  of  the  alveolus,  the  elastic  tissue  is  formed  into  a  thick 
ring.  In  the  meshwork  of  the  elastica  of  an  alveolus  is 
found  a  dense  plexus  of  capillaries.  The  amount  of  elastica 
allows  a  great  increase  in  size  of  the  air  sacs  (2  to  3  times). 

From  W.  S.  Miller's  careful  studies  on  the  structure  of 
the  lungs,  the  terminal  bronchioles  terminate  as  follows : 
Each  respiratory  bronchiole  divides  into  one  or  more  alve- 
olar ducts,  which  widen  at  their  outer  ends.  Each  duct  opens 
into  several  vestibula;  from  each  vestibulum,  a  number  of 
atria  open,  which,  in  turn,  communicate  with  the  air-sacs,  or 
alvei,  on  the  walls  of  which  are  the  alveoli. 

The  circulatory  system  is  peculiar.  As  in  the  liver,  tzvo 
sets  of  vessels  enter,  the  pulmonary  and  bronchial,  but,  un- 
like those  of  the  liver,  they  do  not  unite  to  form  a  single  ves- 
sel, but  remain  individual.  There  is  some  anastomosis  be- 
tween the  two  sets  of  vessels. 

The  pulmonary  artery  conveys  the  blood  to  be  oxygen- 
ated, and 'is  the  nutrient  vessel  of  the  functionating  epithelial 
cells.    It  branches  at  the  root,  and  the  divisions  follow  those 


150  RESPIRATORY    SYSTEM. 

of  the  bronchus  very  closely.  Between  the  lobules,  its 
branches  are  the  interlobular  divisions,  and  these  penetrate 
the  lobules  to  form  the  densest  capillary  plexus  of  the  body, 
within  the  elastica  of  the  alveoli.  Here,  the  endothelial  cells 
of  the  capillary,  and  the  squamous  epithelial  cell  of  the  alve- 
olus, separate  the  blood  from  the  air.  Such  an  exceedingly 
thin  membrane  allows  the  interchange  of  oxygen  and  effete 
gases,  and  also  the  absorption  of  nutrient  matter  by  the  epi- 
thelial .cells,  and  the  outward  passage  of  the  waste  matter. 
The  blood  is  collected  by  the  venous  radicals  of  the  pul- 
monary vein,  and  these  unite  to  form  the  interlobular 
branches,  that  ultimately  form  the  pulmonary  veins. 

The  bronchial  artery  branches  somewhat  as  the  pulmonary 
artery,  but  its  divisions  do  not  penetrate  to  the  same  degree. 
They  enter  the  lobule  and  form  capillaries  around  the  vessels 
and  ducts  here  and  nourish  them,  but  not  the  respiratory  epi 
thelium.  The  capillaries  lie  in  the  interlobular  connective 
tissue,  and  supply  the  vessels  there  with  nutrient  material 
Between  these  two  sets  of  vessels,  the  pulmonary  and  bron- 
chial arteries,  there  is  some  anastomosis,  so  that  the  pulmon- 
ary veins  carry  some  of  the  bronchial  arterial  blood  from 
the  lungs.  The  bulk  of  the  bronchial  blood,  however,  is  col- 
lected by  the  divisions  of  the  bronchial  veins  that  finally 
empty  into  the  vena  azygos,  right  and  left  (or  left  superior 
intercostal). 

The  lymphatics  are  superficial  and  deep;  the  former  lie 
beneath  the  pleurae  and  connect  with  the  deep  plexus.  The 
latter  consists  of  vessels  that  follow  the  blood-vessels  and 
lie  in  the  interlobular  connective  tissue ;  these  have  a  number 
of  lymph  nodes  (bronchial  glands)  in  their  course. 

The  nerves  are  mainly  sympathetic,  though  the  vagus 
sends  branches  to  the  lungs.  They  end  chiefly  in  the  blood- 
vessels. 


THYROID  BODY.  I5I 

The  following  are  the  epithelial  cells  that  line  the  various 
portions  of  the  Respiratory  Tract : 

(  First  Part Stratified  squamous. 

*  "  j  Second  Part Stratified  ciliated. 

Pharynx  ...   Stratified  ciliated. 

r  Epiglottis Stratified  squamous. 

Larynx,  j  Vocal  Cords Stratified  squamous. 

(^Remainder  of  Larynx.  Stratified  ciliated. 

Trachea Stratified  ciliated. 

Bronchi S^tratified  ciliated. 

Bronchial  Tubes Stratified  ciliated. 

(  Simple  ciliated. 

Bronchioles J  Simple  columnar. 

(_  Simple  squamous  (respiratory). 

Alveolar  Ducts Simple  squamous  (respiratory). 

Alveoli Simple  squamous  (respiratory). 


THYROID  BODY. 

The  Thyroid  Body  is  a  ductless,  compound  tubular  gland, 
and  consists  of  tv^^o  large  lateral  lobes  united  by  a  narrow 
band,  the  middle  lobe,  or  isthmus. 

The  organ  is  surrounded  by  a  capsule  that  sends  in  trabe- 
culae,  which  divide  the  gland  into  lobes  and  lobules.  These 
divisions  are  irregular,  and  the  loibules  are  composed  of  a 
number  of  short  tubules,  sometimes  called  follicles.  Each 
tubule  is  lined  by  cuboidal  epithelial  cells  that  rest  upon  a 
basement  membranej  outside  of  this  is  the  intralobular,  or 
intertubular,  connective  tissue  that  supports  the  blood-ves- 
sels. In  the  tubules  is  seen  a  peculiar,  homogeneous  sub- 
stance, the  colloid  substance,  that  is  supposedly  the  result  of 
the  activity  of  the  cells.  It  has  a  yellowish  color,  and  as 
blood  cells  are  frequently  seen  in  it,  the  color  may  be  due  to 
the  hemoglobin  from  these.  Sometimes,  the  colloid  material 
is  shrunken,  and  then  its  edges  are  crenated ;  in  such  tubules, 


152  RESPIRATORY   SYSTEM. 

the  epithelial  cells  are  drawn  away  from  the  basement  mem- 
brane. 

Blood-vessels    are    numerous,    and    dense    plexuses    are 
formed  around  the  tubules.     It  is  thought  that  the  colloid 


,^X^ 


^ 


Fig.  60. — Section  of  Human  Thyroid  Gland. 

a.    Epithelium ;    6.    basement   membrane ;    c.    colloid   substance ;    d.    inter- 
lobular connective  tissue  ;  e.  interlobular  vein. 


material  may  represent  an  internal  secretion  that  is  absorbed 
by  the  blood-vessels,  or  perhaps  the  lymphatics. 

The  lymphatics  are  numerous,  and  lie  between  the  tubules. 
They  often  contain  some  of  the  colloid  substance. 

PARATHYROIDS. 

The  Parathyroids  are  usually  four  in  number,  two  of 
which  lie  in  close  relation  with  each  lateral  lobe  of  the  thy- 
roid.   They  are  small,  and  the  epithelial  cells  are  usually  of 
the  glandular  type,  and  are  arranged  m{groups,  or  chains^^.^ 
forming  a  network,  or  ez^en  tubules.     Between  the  cells  is 


PARATHYROIDS. 


153 


white  fibrous  connective  tissue  that  supports  quite  a  capilj 
lary  plexus.  Occasionally,  colloid  material  is  seen  in  the 
tubules.  When  the  thyroids  are  removed  and  the  parathy- 
roids remain,  they  hypertrophy  and  carry  on  the  function 
of  the  removed  ors^ans. 


CHAPTER  XII. 


THE    URINARY   SYSTEM. 

The  Urinary  Organs  comprise  the  Kidneys,  Ureters, 
Bladder  and  Urethra.  On  account  of  its  proximity  to  the 
kidney,  the  Adrenal  will  also  be  considered. 

The  Kidney  is  a  compound  tubular  gland,  and,  next  to 
the  liver,  the  largest  in  the  body.  It  lies  in  a  mass  of  adipose 
tissue,  the  perirenal  fat,  from  which  it  is  readily  separated. 
Some  of  this  fat  persists  even  when  the  animal  dies  of  starv- 
ation. 

The  kidney  is  surrounded  by  a  thin  capsule  of  white 
fibrous  tissue  that  normally  strips  readily  from  the  organ. 
This  is  of  great  importance,  when  the  organ  is  studied  patho- 
logically. Beneath  the  capsule  is  the  kidney  parenchyma 
that  consists  of  a  great  number  of  tubules,  the  uriniferous 
tubules,  that  have  a  very  irregular  course.  Along  the  in- 
ternal margin  is  a  depression  or  notch,  the  hilus^  at  which 
the  vessels  enter  and  leave. 

When  the  organ  is  sectioned,  upon  microscopic  examina- 
tion it  is  seen  to  consist  of  an  outer  margin,  the  cortex,  and 
an  inner  broader  portion,  the  medulla.  Just  within  the  hilus 
is  seen  a  space,  the  sinus,  containing  the  pelvis  and  the  main 
branches  of  the  renal  artery  and  vein. 

The  cortex  constitutes  the  outer  third  of  the  organ,  and 
is  further  subdivided  into  medullary  rays  and  labyrinth. 
This  division  is  represented  by  the  alternating  dark  and 
light  bands,  which  are  at  right  angles  to  the  capsule,  and 
gives  a  striated  appearance  to  the  cortex. 

The   MEDULLARY   RAYS,   Or  PYRAMIDS   OF   FeRREIN,   COnsist, 

microscopically,  of  the  straight  portions  of  the  tubules  that 
extend  from  the  medulla  into  the  cortex,  surrounded  by  the 

154 


KIDNEY. 


i:).-) 


intertubular,  or  interstitial  reticulum.  They  never  extend 
to  the  capsule,  but  diminish  in  width  as  the  outer  portion  of 
the  cortex  is  approached. 


Fig.  G1. — Sectiox  of  Human  Kidney  showing  Cortex  and  Medulla. 
a.  Capsule  ;  h.  cortex  ;  c.  medulla  :  d.  labyrinth  ;  e.  medu,llary  ray  ;  /.  Mal- 
pigliian  bodies  ;  g.  area  in  which  Malpighian  bady  has  dropped  out ; 
h.  capsule  of  Bowman  ;  i.  glomerulus  :  k.  afferent  arteriole  ;  I.  neck  of 
uriniferous  tubule  :  m,  tubules^f  labyrinth  :  n.  longitudinal  sections 
of  collecting  tubules  ;   o.   cross-sections  of  collecting  tubules. 


I- 


The  LABYRINTH  Hcs  betwceii  the  medullary  rays,  and  is 

•mposed    of   the    Malpighian    corpuscles,    the    starting 

oints  of  the  tubules,  and  the  convoluted  portions  of  the 


156  THE    URINARY    SYSTEM. 

urinif eroiis  tubules.  These  are  supported  by  the  interstitial 
connective  tissue  that  contains  the  blood-vessels. 

The  Malpighian  corpuscles  are  found  only  in  the  cor- 
tex, and  here  are  limited  to  the  labyrinih.  Each  one  con- 
sists of  a  tuft  of  arterial  capillaries,  the  glomerulus^  or 
Malpighian  tuft^  surrounded  immediately  by  a  delicate 
double  membrane  of  simple  squamous  cells,  resting  upon  a 
basement  membrane.  The  inner  layer  lies  upon  the  tuft, 
and  the  outer  forms  the  wall  of  the  tubule.  This  membrane 
is  Bowman's  capsule,  and,  with  the  tuft,  comprises  the 
Malpighian  corpuscle.  The  tuft  itself  is  not  a  simple 
structure.  The  arteriole,  upon  entering,  divides  into  a  num- 
ber of  branches,  each  of  which  forms  a  set  of  capillaries. 
This  apparent  lobulation  is  quite  distinct. 

The  medulla  is  sharply  outlined  from  the  cortex,  micro- 
scopically, by  the  absence  of  Malpighian  corpuscles  and  the 
regularity  of  the  tubules.  At  the  junction  are  to  be  found 
the  great  vessels,  and  this  portion  is  called  the  boundary  zone. 
The  medulla  consists  of  the  medullary,  or  Malpighian 
pyramids,  separated  from  one  another  by  the  columns  of 
Bertinl 

The  Malpighian,  or  medullary  pyramids  are  ten  to  six- 
teen in  number.  Their  bases  continue  with  the  cortex,  and 
their  apices  are  directed  towards  the  hilus  and  project  into 
the  sinus.  Each  consists  of  a  large  number  of  straight 
tubules  that  become  fewer  in  number  as  the  apex  is  reached, 
where  but  fifteen  to  twenty  are  present..  These  are  the 
PAPILLARY  DUCT^  or  DUCTS  OF  Bellini.  The  tubulcs  are 
supported  by  reticulum,  in  which  the  capillaries  are  found. 

The  PYRAMIDS  are  separated  from  one  another  by  a  narrow 
band  of  tissue,  that,  near  the  apices,  is  chiefly  white  fibrous; 
towards  the  bases,  the  parenchyma  begins  to  enter  into  its 
formation.    This  is  the  column  of  Bertini,  and  within  it  are 


KIDNEY.  157 

the  large  vessels  that  pass  from  the  sinus  to  the  boundary 
zone. 

The  PYRAMIDS  represent  the  embryonal  condition  when 
the  whole  organ  consisted  of  lobes.  At  birth,  usually,  the 
bases  of  the  lobes  have  fused  to  form  the  cortex,  but  the 
inner  ends  never  reach  that  condition.  The  columns  of 
Bertini  then  represent  the  interlobar  connective  tissue  and 
spaces.     In  some  animals  the  lobulation  never  disappears. 

The  uriniferous  tubule  has  a  very  peculiar  and  convoluted 
course.  It  starts  in  the  cortex,  and  passes  into  the  medulla, 
to  return  to  the  cortex  for  its  final  passage  through  the 
medulla.  It  originates  at  the  Malpighian  corpuscle,  which 
is  merely  the  invaginated  end  of  the  tubule,  containing  a  tuft 
of  capillaries.  From  this,  the  presence  of  a  double  capsule 
can  be  readily  understood.  The  corpuscle  is  succeeded  by 
a  narrow  constricted  portion,  the  neck,  lined  by  simple 
squamous  cells  lying  upon  a  basement  membrane,  and  sup- 
ported by  interstitial  connective  tissue,  which  continues 
throughout.  The  next  portion,  the  proximal,  or  first  con- 
voluted tubule,  as  its  name  indicates,  is  very  convoluted  and 
irregular.  This  part  lies  in  the  labyrinth,  and  is  lined  by 
cuboidal  cells,  in  which  the  protoplasm  is  granular  and  the 
cell  boundaries  indistinct.  That  part  of  the  cell  near  the 
lumen  is  striated.  This  continues  as  the  descending  limb 
OF  Henle's  loop,  which  passes  into  the  medulla  and  is  suc- 
ceeded by  the  loop  and  the  ascending  limb.  The  descending 
limb  and  the  loop,  at  times,  are  lined  by  simple  squamous 
cells,  which  are  so  flat  that  the  nuclei  project.  The  ascend- 
ing limb,  and,  according  to  some,  the  loop,  contains  simple 
cuboidal  cells,  which  may  begin  as  flat  cells.  The  protoplasm 
■)f  these  is  striated.  The  continuation  of  the  ascending  is 
the  second,  or  distal,  convoluted  tubule,  and  here  the  cells 
are  cuboidal  and  irregular,  and  the  protoplasm  granular  and 


158  THE    URINARY    SYSTEM. 

Striated.  This  portion  lies  in  the  labyrinth,  and  is  succeeded 
by  a  short,  curved  portion,  the  arched  connecting  tubule, 
that  connects  the  irregular  with  the  straight  collecting 
tubule.  These  are  lined  by  simple  columnar  cells  that  become 
longer  as  the  papillae  are  approached.  The  protoplasm  of 
these  is  clear,  and  not  striated.  The  straight  tubules,  as 
they  approach  the  apex  of  the  pyramid,  unite  to  form  fifteen 
to  eighteen  large  excretory  tubules,  the  ducts  of  Bellini,  or 
PAPILLARY  DUCTS.    These  are  lined  by  long  columnar  cells. 

The  various  portions  of  the  uriniferous  tubule  are  dis- 
tributed as  follows : 

Cortex.  In  the  labyrinth  are  found  the  Malpighian 
corpuscles,  neck,  first  and  second  convoluted  iubules.  In 
the  medullary  rays,  the  upper  ends  of  the  descending  and 
ascending  limbs  of  Henle's  loop  and  straight  collecting  tub- 
ules, and  the  arched  connecting  tubule. 

Medulla.     The  lower  ends  of  the  descending  and  ascend 
ing  limbs  and  the  loop  of  Henle  and  the  straight  collecting 
tubules  and  papillary  ducts. 

The  diameter  of  the  dififerent  parts  of  the  tubule  varies. 
The  Malpighian  body  is  large,  measuring  120  to  200 
microns.  The  neck  averages  about  75  microns,  and  the 
proximal  convoluted  tubule  is  quite  irregular,  but  the  av- 
erage is  about  40  microns.  The  descending  limb  is  quite 
narrow,  10  to  ij  microns,  and  the  ascending  limb  about  25. 
In  the  SECOND  convoluted  tubule,  the  diameter  again  in- 
creases, averaging  40  to  45  microns.  From  the  beginning 
of  the  straight  tubule  to  the  end,  the  diameter  progres- 
sively increases,  so  that  the  papillary  ducts  may  have  a 
diameter  of  200  microns. 

The  blood-vessels  have  a  characteristic  distribution.  The 
renal  artery  passes  through  the  hilus  and  enters  the 
SINUS,  where  it  divides  into  a  number  of  branches,  of  which 


KIDNEY. 


159 


the  greater  number  supply  the  anterior  pyramids,  and  the  an- 
terior portions  of  the  posterior  pyramids.  The  branches  that 
go  to  the  anterior  pyramids  carry  the  greater  part  of  this 
blood.  The  rest  of  the  kidney  is  supplied  by  the  posterior 
branches.  The  branch  that  supplies  each  pole,  derived  from 
the  anterior  division,  divides  into  anterior,  middle  and  pos- 


FiG.  62. — Section  of  Injected  Kidney  of  Guinea-Pig. 


1.  Interlobular  (cortical)  artery;  2.  afferent  vessel;  3.  efferent  vessel; 
4.  capillary  network  in  medullary  ray  ;  5.  capillary  network  in  laby- 
rinth ;  6.  interlobular  (cortical)  vein  {Stokr's  Histology). 


tcrior  branches,  which  are  in  no  way  united.  The  trunks 
pass  up  through  the  columns  of  Bertini,  where  small 
branches  are  given  off  to  the  vessels  and  tissues,  as  the  in- 
terlobar BRANCHES.  Thcse  branches  pass  to  the  boundary 
::one,  where  they  arch  between  the  cortex  and  medulla,  form- 
ing the  ARTERIAL  ARCHES,  or  ARCADE.    From  the  cortical  side 


l6o  THE    URINARY    SYSTEM. 

of  the  arch,  the  cortical,  or  interlobular,  arteries  are  sent 
towards  the  capsule ;  from  these,  small  arterioles,  afferent, 
pass  to  the  Malpighian  corpuscles,  enter  and  form  several 
smaller  branches,  each  of  which  breaks  into  a  capillary  tuft 
From  this,  it  will  be  seen  that  the  Malpighian  tuft  consists 
of  several  bunches  of  capillaries.  Each  capillary  group  is 
separate,  and  the  vessels  unite  to  form  arterioles  that  leave 
the  tuft  as  a  single  vessel,  the  efferent  arteriole.  The  blood 
is  still  arterial.  The  efferent  arterioles  soon  form  dense 
PLEXUSES  OF  capillaries  around  the  tubules  of  the  laby- 
rinth and  medullary  rays.  Those  capillaries  near  the  boun- 
dary zone  pass  into  the  medulla  and  surround  the  tubules 
there.  The  capillaries  become  venous  in  character,  and 
unite  with  others  to  form  the  interlobular  veins.  The 
cortical  artery  continues  to  the  capsule,  where  it  forms  a 
star-shaped  mass  of  venules,  the  venae  stellatae.  These 
are,  in  reality,  the  starting  points  of  the  interlobular 
veins,  which  run  parallel  to  the  arteries  of  the  same  name, 
and  empty  into  a  venous  arcade  that  is  formed  at  the 
boundary  zone  by  the  union  of  the  large  vessels.  Such  is 
"  the  blood  supply  of  the  cortex. 

The  MEDULLA  receives  its  blood  from  the  under  surface 
of  the  arterial  arch.  The  arterioles  given  off  have  a  straight 
course,  and  are  the  arteriolae  rectae.  They  very  soon 
break  up  into  capillaries  that  surround  the  tubules  of  the 
medulla.  These  continue  as  venus  radicals  that  unite  to 
form  straight  veins,  venae  rectae,  which  empty  into  the 
VENOUS  ARCH  on  its  concave  surface. 

The  VENOUS  ARCHES  unite  at  the  columns  of  Bertini,  and 
pass  down  these,  parallel  to  the  arteries,  as  the  interlobar 
VEINS.     In  the  sinus,  they  unite  to  form  the  renal  vein. 

The  vessels  of  the  kidney  communicate  with  those  of  the 
perirenal  fat,  through  the  vessels  of  the  capsule.    This  is  of 


PELVIS    OF    KIDNEY.  l6l 

importance.  Direct  anastomoses  between  arterial  and  venous 
vessels  occur  in  this  organ. 

The  LYMPHATICS  Comprise  a  capsular  set,  cortical  and  me- 
dullary plexuses.  The  capsular  vessels  empty  into  those  of 
the  cortical  plexus.  These,  in  turn,  empty  into  those  of  the 
medullary  plexus,  the  vessels  of  which  follow  the  blood- 
vessels, emerge  at  the  hilus,  and  pass  to  the  neighboring 
lymph  glands. 

The  nerves  are  derived  from  both  systems.  They  follow 
the  vessels  and  envelop  them  in  networks  to  the  smallest 
divisions.  Some  supply  the  pelvis,  and  others  pass  to  the 
tubules,  and,  apparently,  enter  the  epithelium. 

THE  EFFERENT  APPARATUS. 

The  Efferent  Apparatus  consists  of  the  Pelvis,  Ureter, 
Bladder  and  Urethra. 

The  Pelvis  is  the  upper,  expanded  portion  of  the  ureter, 
and  lies  in  the  sinus.  It  is  very  irregular,  and  is  divided  into 
two  or  three  main  portions,  the  j[nfu_ndibula,  which  are 
arranged  in  little  cup-like  structures  around  the  apices  of 
Malpighian  pyramids.  These  are  the  calyces,  and  they 
are  equal  in  number  to  the  pyramids.  The  three  coats, 
MUCOUS,  MUSCULAR  and  fibrous,  extend  throughout  the 
ureter  and  bladder. 

The  MUCOUS  membrane  consists  of  transitional  cells, 
basement  membrane  and  tunica  propria.  The  epithelial  cells 
are  not  all  regular,  as  those  of  the  transitional  variety  are 
supposed  to  be.  The  upper  cells  are  usually  somewhat 'flat- 
tened, and  almost  squam.ous.  Beneath  these,  they  are  some- 
what larger,  and  more  or  less  pear-shaped,  while  the  lowest 
cells  are  polyhedral.  The  tunica  propria  consists  of  delicate 
fibro-elastic  tissue,  in  which  adenoid  tissue  may  be  seen. 

The  MUSCULAR  coat  consists  of  smooth  muscle  fibres  that 
are  not  distinctly  arranged  into  layers. 


l62 


THE    URINARY    SYSTEM. 


The  FIBROUS  coat  is  the  supportive  coat,  and  is  composed 
of  white  fibrous  tissue. 

URETER. 
The  Ureter  is  the  small  tube  connecting  the  kidney  and  the 
bladder,  which  organ  it  enters  at  an  acute  angle.     Its  coats 
are  quite  distinct. 


Fig.  G3. 
A.  Cross-section  of  Human  Ureter — a.  lumen  ;  h.  epithelium  ;  c.  basement 
membrane ;  d.  longitudinal  fold  of  mucosa ;  e.  tunica  propria ;  /.  inner 
longitudinal  muscle ;  g.  oater  circular  muscle ;  h.  vessels ;  i.  fib- 
broi.s  coat.  B.  Cross  Section  of  Segment  of  Human  Bladder — a.  mu- 
cous coat ;  &.  submucous  coat ;  c.  fibrous  coat ;  d.  transitional  epi- 
thelium;  e.  basement  membrane:  f.  tunica  propria;  g.  blood-vessels; 
h.  white  fibrous  tissue  ;  i.  inner  longitudinal  muscle  ;  fc.  middle  circu- 
lar muscle ;  I.  white  fibrous  tissue ;  m.  outer  longitudinal  muscle ; 
n.  venule  ;  o.  arteriole  ;  p.  adipose  tissue. 


The  MUCOSA  resemble  that  of  the  pelvis,  with  which  it 
is  continuous.  The  epithelial  cells  have  the  same  appear- 
ance, but  the  tunica  propria  sometimes  sends  delicate  fibres 
up  into  the  epithelial  layer.  These  fibres  lie  between  the 
cells.     In  it  are  found  diffuse  lymphoid  tissue  and  some 


BLADDER.  163 

racemose  glands.  The  whole  coat  is  usually  thrown  into 
longitudinal  folds. 

The  MUSCULAR  coat  consists  of  smooth  muscle  tissue,  ar- 
ranged in  definite  layers.  The  inner  consists  of  longitudinal, 
and  the  outer  of  circular  fibres.  Occasionally,  at  the  lower 
end,  there  is  added  an  external  longitudinal  layer,  which  con- 
tinues into  the  bladder. 

The  FIBROUS  coat  does  not  differ  from  that  of  the  pelvis. 

BLADDER. 

The  Bladder  is  a  muscular  sac  that  acts  as  a  reservoir  for 
the  urine.  It  consists  of  fundus  or  body,  and  a  small  con- 
stricted portion,  the  neck,  which  continues  as  the  urethra. 

The  MUCOUS  coat  resembles  that  of  the  ureter  in  structure. 
The  cells  may  be  somewhat  flatter.  Often,  in  the  ureter  and 
bladder  of  children  at  birth,  and  older  fetuses,  the  cells  are 
all  of  the  polyhedral  type,  and  represent  a  typic  layer  of 
transitional  cells.  In  urinary  examinations,  it  is  practically 
impossible  to  tell  the  cells  of  the  pelvis,  ureter  and  bladder 
from  one  another.  The  tunica  propria  contains  diffuse  aden- 
oid tissue,  and  even  solitary  follicles,  also  racemose  glands. 

The  mucosa  is  loosely  attached  to  the  muscular  coat,  ex- 
cept at  a  small  triangular  area  near  the  neck.  This  space 
has  for  its  apex,  the  urethral  opening,  and  for  its  basal  angles, 
the  ureteral  orifices.  A  line,  connecting  the  two  latter, 
forms  the  base.    This  area  is  the  trigomtm  vesicae. 

The  MUSCULAR  coat  is  composed"  of  smooth  muscles.  This 
is  arranged  as  inner  longitudinal,  middle  circular  and  outer 
longitudinal  layers.  All  of  the  layers  interlace,  more  or  less, 
thereby  giving  a  peculiar  appearance  to  this  coat.  At  the 
neck,  the  circular  fibres  become  quite  pronounced,  and  con- 
stitute  the  sphincter  of  the  bladder. 

The  FIBROUS  coat  supports  the  others,  and  prevents  undue 
dilatation. 


164  THE    URINARY    SYSTEM. 

The  blood-vessels  lie  in  the  outer  portion  of  the  tunica 
propria  of  the  above  organs,  and  from  these  a  very  close  net- 
work of  capillaries  is  formed  beneath  the  epithelium,  and  in 
the  muscular  coat.  These  vessels  are  accompanied  by  the 
lymphatics. 

The  nerves  are  chiefly  sympathetic,  and  ganglia  are  not 
uncommon.  Many  of  the  nerve  fibres  end  beneath  the 
epithelium. 

The  male  Urethra  is  many  times  longer  than  that  of  the 
female.  In  the  female,  the  structure  is  quite  simple,  and  it 
will  be  first  considered. 

The  female  Urethra  is  lined  by  transitional  cells,  except 
at  its  outer  end,  where  the  stratified  squamous  cells  of  the 
skin  enter  into  its  structure.  The  transitional  cells  are  some- 
times quite  flattened.  Some  writers  describe  a  simple  colum- 
nar layer  in  the  middle  portion.  The  basement  membrane 
rests  upon  a  papillated  tunica  propria,  in  which  are  found  the 
glands  of  Littre;  these,  in  the  female,  are  not  very  numerous. 

The  MUSCULAR  coat  consists  of  smooth  muscles,  arranged 
as  inner  longitudinal  and  outer  circular  layers,  separated  by 
an  intermuscular  layer  of  white  fibrous  tissue. 

The  male  Urethra  is  more  complex,  and  is  divided  into 
three  portions,  prostatic,  the  continuation  of  the  bladder; 
the  MEMBRANOUS,  that  portion  beneath  the  symphysis  pubis, 
and  the  penile. 

The  PROSTATIC  part  is  lined  by  transitional  cells  that  are 
continued  from  the  bladder.  In  the  membranous  portion, 
stratiHed  columnar  cells  are  present,  and  these  become  simple 
in  the  penile  division.  Just  before  the  outlet,  or  meatus,  is 
reached,  the  urethra  dilates,  and  this  portion  is  called  the 
fossa  navicularis.  It  is  lined  by  stratified  squamous  cells. 
The   cells   are   all    supported   by  basement  membrane   and 


URETHRA.  165 

tunica  propria,  which  consists  of  white  fibrous  tissue,  in 
which  the  glands  of  Littrc  are  very  numerous. 

The  MUSCULAR  tissue  is  Hke  that  of  the  female  urethra, 
and  continues  to  the  penile  portion,  where  it  disappears.  In 
the  membranous  part,  the  muscular  coat  is  reinforced  by  the 
compressor  urethrae  muscle,  which  tapers  towards  the  pro- 
static and  penile  divisions. 

The  FIBROUS  coat  consists  of  white  fibrous  tissue,  and 
strengthens  the  urethra. 

Capillaries  are  numerous  in  the  mucosa,  and  the  vessels 
are  followed  by  the  nerves  and  lymphatics.  The  nerves  end 
in  the  tunica  propria,  just  beneath  the  epithelium. 

The  various  portions  of  the  Urinary  System  are  lined  by 
the  following  cells : 

Kidney. 
Uriniferous  Tubule: 

Malpighian  Corpuscle Simple  squamous. 

Neck ,  . . .  Simple  squamous. 

First  Convoluted  Tubule.  . . .  Cuboidal  to  columnar. 

Descending  Limb Simple  squamous. 

Loop  of  Henle Simple  squamous  or  low  cuboidal. 

Ascending  Limb Low  cuboidal. 

Second  Convoluted  Tubule..  Cuboidal  to  columnar. 

Arched  Connecting  Tubule.  .Cuboidal. 

Straight  Collecting  Tubule.  Columnar. 

Papillary  Ducts Tall  columnar. 

Pelvis Transitional. 

Ureter Transitional. 

Bladder Transitional. 

TT  T-  (  Transitional. 

Urethra.      Female \  ^       ._    , 

(  btratined  squamous. 

Male 


L 


First  Part Transitional. 

Second  Part Stratified  columnar. 

Third  Part Simple  columnar. 

Fossa  Navivularis Stratified  squamous. 


l66  THE    URINARY    SYSTEM. 

SUPRARENAL  BODY. 

The  Suprarenal  Body,  or  Adrenal,  is  a  ductless  gland.  It 
lies  at  the  upper  pole  of  the  kidney,  and  has  a  yellow  color. 
Upon  section,  it  shows  a  yellow  external  layer,  and  a  dark 
centrum. 

The  organ  is  surrounded  by  a  capsule  of  white  fibrous 
tissue,  in  which  involuntary,  nonstriated  muscle  may  be 
found.  .Beneath  this  is  the  parenchyma,  which  consists  of 
Cortex  and  Medulla. 

The  Cortex  consists  of  three  zones  of  epithelial  cells,  the 

ZONA    GLOMERULOSA,    ZONA    FASCICULATA    and   ZONA   RETICU- 
LARIS. 

The  ZONA  GLOMERULOSA  Hcs  just  beneath  the  capsule,  and 
is  composed  of  several  rows  of  cell-groups,  oval  or  circular 
in  outline,  surrounded  by  capillaries  and  reticulum.  The 
cells,  mostly  large  and  polyhedral,  contain  a  considerable 
number  of  fat  globules. 

Beneath  this  zone,  the  cells  are  arranged  in  columns  of 
twos,  called  the  zona  fasciculata.  These  cells  resemble 
the  above,  but  the  nuclei  are  on  the  capillary  side  of  the  cells. 
The  columns  are  separated  from  one  another  by  reticulum, 
supporting  many  capillaries. 

The  zona  reticularis  is  composed  of  an  irregular  net- 
work of  cells  formed  by  the  anastomosis  of  the  columns. 
These  cells  are  usually  smaller  and  outlines  distinct.  The 
nuclei  are  large,  and  the  protoplasm  pigmented. 

The  Medulla  is  usually  separated  from  the  cortex  by  a 
layer  of  large,  smooth  cells.  Beneath  this  layer,  the  cells 
are  arranged  in  irregular  groups,  and  chains  surrounded  by 
reticulum  and  capillaries.  These  cells  are  small,  and  their 
outlines  are  indistinct.  They  color  very  deeply  with  chromi- 
um salts.     Nerve  cells  are  also  present. 


ADRENAL. 


167 


The  blood-vessels  are  quite  numerous,  and  apparently  ab- 
sorb the  secretion  of  the  gland.  They  form  a  plexus  in  the 
capsule,  from  which  the  arterial  branches  penetrate  the  cor- 
tex, where  they  form  many  capillaries  that  surround  the 
cells  quite  closely.     These  capillaries  empty  into  thin-walled 


Pig.  64. — Section  of  the  Human  Adrenal. 

A.  Cortex  ;  B.  Medulla ;  C.  Capsule.  1.  Zona  glomerulosa  ;  2.  zona  fasci- 
culata  ;  3.  zona  reticularis ;  4.  cell  cords  of  the  medulla  ;  5.  cross-sec- 
tion of  a  nerve  ;  6.  ganglion  cells ;  7.  cross-sections  of  smooth  muscle 
fibres;  8.  cross-sections  of  veins   {Stdhr's  Histology). 


venous  radicals  in  the  outer  portion  of  the  medulla,  and 
from  them  veins  are  formed  that  do  not  anastomose  with 
one  another,  but  empty  into  the  central  veins.  The  medul- 
lary capillaries  are  derived  from  the  capsular  vessels  that  pass 
to  the  medulla  through  the  cortex  without  branching.    They 


l68  THE    URINARY    SYSTEM. 

unite  to  form  the  above-named  veins,  which  are  two  or  four 
in  number. 

The  lymphatics  follow  the  blood-vessels  closely.  They  lie 
between  the  cell-groups,  and  even  penetrate  the  columns, 
and  end  between  the  cells. 

The  nerves,  both  medullated  and  nonmedullated,  are 
numerous.  A  plexus  in  the  capsule  sends  branches  into  the 
cortex,  where  plexuses  are  formed  around  the  vessels. 
Branches  pass  from  the  capsular  plexus  to  the  medulla, 
where  rich  plexuses  are  formed  around  the  cells  and  veins. 
Sympathetic  ganglia  are  also  present. 


CHAPTER  XIII. 


THE  MALE  GENITAL  SYSTEM. 

The  Male  Generative  Organs  form  a  very  complex  sys- 
tem. They  comprise  the  Testicle,  Epididymis,  Vas  Defer- 
ens, Seminal  Vesicles,  Ejaculatory  Duct,  Prostate, 
Glands  of  Cowper  and  the  Penis. 

The  Testicle  is  another  compound  tubular  gland_.  It  is 
surrounded  by  an  unusually  thick  capsule  called  the  tunica 
ALBUGiNEA,  which  is  composcd  of  bundles  of  white  fibrous 
tissue  that  interlace  so  as  to  form  a  very  tough  and  promi- 
nent covering.  From  its  inner  surface,  prolongations,  or 
trabeculae,  pass  into  the  center  of  the  organ  to  divide  it  ir- 
regularly into  compartments.  These  trabeculae  all  converge 
at  the  posterior  portion  of  the  organ,  where  the  capsule  is 
very  thick,  forming,  at  this  point,  a  thickened  miass  called  the 
CORPUS  HiGHMORi,  or  MEDIASTINUM  TESTIS.  Here  a  num- 
ber oiFTubules,  to  be  described  later,  are  found. 

The  TUNICA  VAGINALIS  TESTIS  is  a  SEROUS  MEMBRANE  that, 

at  one  time,  was  continuous  with  the  peritoneum.  It  covers 
almost  the  entire  organ,  and  is  attached  to  the  tunica  al- 
buginea,  and  constitutes  the  visceral  layer  of  the  tunica  vag- 
inalis. It  is  reflected  over  the  inner  surface  of  the  scrotum 
as  the  parietal  layer.  Some  writers  consider  this  membrane 
part  of  the  tunica  albuginea,  and  describe  it  as  such,  but  as 
it  is  genetically  different,  it  should  be  considered  a  separate 
covering. 

The  PARENCHYMA  of  the  testicle  is  made  up  of  tubules, 
which,  like  those  of  the  kidney,  are  very  convoluted,  and  con- 
sist of  secretory  and  conductive  portions.  These  tubules  are 
the  SEMINIFEROUS  TUBULES,  and  are  collected  into  groups 
which  correspond  to  lobules.     These  groups,  limited  by  the 

169 


170 


THE    MALE  GENITAL   SYSTEM. 


connective  tissue  of  the  tunica  albuginea  that  extends  to  the 
corpus,  constitute  the  compartments  of  the  testicle. 

The  COMPARTMENTS  Contain  a  large  number  of  very  convo- 
luted tubules,  in  which  the  spermatozoa  are  formed ;  these 
are  the  seminiferous  tubules  proper,  and  they  are  suppos- 


FiG.  65. — Human  Testicle. 

A.  Peripheral  portion  of  the  testicle  showing  the  capsule  and  tubules — a. 
tunica  albuginea ;  &.  blood-vessel ;  c.  membrana  propria  of  tubule ; 
d.  interstitial  cells ;  e.  spermatogenetic  cells ;  f.  lumen  of  longitud- 
.inal  tubule.  B.  Single  seminiferous  tubule  hignly  magnified — a.  tunica 
propria ;  h.  basement  membrane ;  c.  spermatogonia ;  d.  cells  of  Ser- 
toli :  e.  mother  and  daughter  cells :  f.  spermatids ;  g.  spermatozoa. 
C.  Spermatozoa  highly  magnified.     D.  Tubule  of  the  epididymis. 


ed  to  end  blindly  beneath  the  capsule.  According  to  some, 
however,  they  anastomose,  and  so  form  a  set  of  communi- 
cating tubules,  which  pass  toward  the  apex  of  a  compart- 
ment, where  they  unite  to  form  10  to  15  straight  tubules 
that   are  conductive  in    function.      These   are   the   tubuli 


I 


TESTICLE  171 

RECTI,  which  pass  into  the  mediastinum,  where  they  anasto- 
mose to  form  a  network  called  the  rete  testis.  In  the  upper 
portion  of  the  mediastinum,  these  tubules  join  to  form  a  few 
vessels  that  pass  toward  the  edge  of  the  corpus  Highmori, 
as  the  VASA  efferentia.  As  these  leave  the  testicle,  they 
become  convoluted  and  dilated  into  cone-shaped  structures 
called  the  coni  vasculosa,  or  globus  major,  of  the  epi- 
didymis. The  coNi  vasculosa  unite  to  form  a  single  tubule 
that  runs  a  very  convoluted  course,  forming  a  narrow  con- 
tinuation of  the  above,  called  the  body  of  the  epididymis.  At 
the  lower  pole  of  the  testicle,  the  mass  formed  by  the  con- 
tinuation of  the  body,  is  somewhat  larger,  and  is  named  the 
GLOBUS  minor.  The  tubule  that  continues  from  this  point 
into  the  abdomen  is  called  the  vas  deferens. 

The  seminiferous  tubules  are  from  140  to  200  microns 
in  diameter,  and  form  the  bulk  of  the  testicle.  Each  con- 
sists of  a  small  amount  of  tunica  propria,  and  a  basement 
membrane,  upon  which  is  found  a  number  of  layers  of  cells. 
The  basal  layer  consists  of  two  varieties,  the  spermato- 
gonia, which  are  the  more  numerous,  and  the  sustentacu- 
LAR  cells,  or  columns  of  Sertoli. 

The  spermatogonia  are  rather  large  cells,  in  which  the 
nuclei  are  mostly  in  the  resting  stage.  The  cells  just  within 
these  are  derived  from  the  spermatogonia,  and  are  the 
mother  cells.  Each  mother  cell  divides  into  two 
daughter  cells,  which,  in  turn,  give  rise  to  the  spermatids. 
from  which  the  spermatozoa  are  developed.  These  layers 
are  not  regular,  as  the  space  within  the  lumen  is  gradually 
filled  by  the  reproducing  cells. 

The  COLUMN  of  Sertoli,  or  sustentacular  cell  is  a  less 
distinct  element.  It  is  pyramidal  in  shape,  and  extends  up 
through  the  various  layers,  and  serves  as  a  support  for  the 
cells  that  are  being  transformed  into  spermatozoa.    For  this 


172  THE    MALE   GENITAL    SYSTEM. 

reason,  it  has  received  the  name  of  sustfntacular  cell. 
Its  protoplasm  is  usually  clear,  though  it  may  contain  pig- 
ment granules.  Its  nucleus  is  pale,  but  the  nucleolus  is  quite 
prominent.     It  plays  an  important  part  in  spermatogenesis. 

Between  the  tubules  lies  the  interstitial  connective 
TISSUE  that  supports  the  blood-vessels,  nerves  and  lymphat- 
ics. It  is  the  variety  of  connective  tissue  called  reticulum, 
and  here  and  there  are  found  groups  of  large  cells  that  con- 
tain coarse  granular  protoplasm.  These  are  the  intersti- 
tial CELLS,  or  CELLS  OF  Leydic.  The  protoplasm  often  con- 
tains pigment,  fat  and  crystalloids.  These  cells  are  probably 
embryonal  remains.  They  are  most  numerous  before  and 
after  the  period  of  sexual  activity. 

The  EXCRETORY  SYSTEM  starts  with  the  tubuli  recti. 
These  are  from  25  to  50  microns  in  diameter,  and  extend  to 
the  apex  of  the  compartment.  They  are  lined  by  simple 
cuboidal,  or  squamous,  cells  that  rest  upon  a  basement  mem- 
brane. 

The  RETE  TESTIS  cousists  of  a  network  formed  from  the 
tubuli  recti,  and  lies  in  the  mediastinum.  These  tubes  have 
a  somewhat  larger  diameter  than  the  foregoing,  but  are 
lined  by  the  same  variety  of  cells. 

The  VASA  EFFERENTiA  are  few  in  number,  and  are  formed 
by  a  union  of  the  tubules  of  the  rete  testis.  The  lining  cells 
are  rather  peculiar  in  that  in  some  areas  they  are  simple 
ciliated,  while  in  others,  nonciliated.  The  basement  mem- 
WanTis  further  supported  by  interstitial,  tissue  that  contains 
some  circularly  arranged  nonstriated  muscle  tissue. 

The  Epididymis  consists  of  a  mass  of  convoluted  tubules 
that  lie  outside  of  the  testicle.  It  is  divided  into  three  por- 
tions, the  globus  major,  or  head:  the  body,  and  the  globus 
minor,  or  tail.  The  globus  major  consists  of  15  to  20  large, 
cone-shaped  tubules  that  are  very  convoluted.    These  tubules 


SPERMATOZOON.  1 73 

are  the  continuations  of  the  vasa  efferentia.  The  cilia  are  the 
largest  in  the  body.  The  body  and  tail  consist  of  a  single 
long  tubule  that  is  very  convoluted. 

The  epididymis  is  surrounded  by  a  dense  sheath  or  cap- 
sule of  white  fibrous  tissue  that  divides  it  into  compartments. 
In  the  globus  major,  the  tubules  in  a  compartment  repre- 
sent the  convolutions  of  one  of  the  coni  vasculosa. 

The  tubules  are  lined  by  stratified  ciliated  cells  that 
rest  upon  a  basement  membrane,  outside  of  which  is  a  dis- 
tinct tunica  propria.  External  to  this  are  two  layers  of 
smooth  muscle  tissue,  one  circularly,  and  the  other  (thin) 
longitudinally,  arranged. 

The  vessels  of  the  testicle. enter  the  corpus  Highmori  and 
inner  layer  of  the  tunica  albuginea,  and  send  branches 
around  the  convoluted  tubules,  especially,  forming  dense 
plexuses. 

The  lymphatics  originate  in  the  capsule  and  around  the 
seminiferous  tubules,  and  pass  to  the  corpus,  and  leave  the 
testicle  from  that  point. 

The  nerves  are  chiefly  sympathetic,  but  possess  no  ganglia. 
They  form  plexuses  around  the  vessels  and  the  tubules  Oc- 
casionally, ganglia  are  found  in  the  epididymis. 

A  Spermatozoon  consists  of  three  main  parts,  head, 
middle-piece  and  tail. 

The  head  is  somewhat  pear-shaped,  when  viewed  from 
the  side,  and  is  4  to  5  microns  long,  and  2  to  3  microns  wide. 
In  its  anterior  end  is  sometimes  seen  the  acrosome,  a  small 
dark  body  derived  from  the  second  centrosome. 

The   middle-piece   is   composed   of   several  portions,   the 

END-KNOB,    AXIAL   FIBRE   and   ENVELOP        The   END-KNOB   IS    a 

globular  mass  that  connects  the  head  with  the  axial  fibre, 
and  is  the  anterior  end  of  the  elongated  centrosome.  The 
AXIAL  FIBRE  is  a  dark  band  that  lies  in  the  center  of  the 


174  THE   MALE  GENITAL   SYSTEM. 

middle-piece  and,  with  the  end-knob,  is  derived  from  the 
larger  centrosome.  The  envelop  is  a  faintly-staining  sheath 
surrounding  the  axial  fibre.  The  middle-piece  is  about  5 
microns  long  and  2  or  3  wide. 

The  tail  consists  of  axial  fibre  and  envelop.  The 
AXIAL  FIBRE  is  the  continuation  of  the  axial  fibre  of  the 
middle-piece,  but  is  not  so  prominent.  It  is  about  5  microns 
longer  than  the  envelop.  The  envelop  is  continuous  with 
that  of  the  middle-piece,  and  has  the  same  characteristics. 
The  tail  measures  about  40  to  50  microns  in  length. 

Spermatogenesis  is  that  peculiar  change  by  which 
spermatozoa  are  formed  from  cells  several  generations  re- 
moved from  the  spermatogonia,  or  original  cell.  The 
spermatogonia,  with  the  columns  of  Sertoli,  form  the  basal 
layer  of  cells  of  the  seminiferous  tubule.  Up  to  the  age  of 
puberty,  these  tubes  are  usually  solid,  or  nearly  so. 

The  Spermatogonia  represent  the  primordial  cells,  and, 
by  division  give  rise  to  the  mother  cells,  or  spermatocytes. 
These  latter  give  rise  to  the  daughter  cells,  or  spermatids, 
which,  by  a  direct  change,  become  spermatozoa.  In  this  last 
division,  the  chromosomes  are  reduced  from  twenty- four  to 
twelve.  Upon  fertilization,  these  twelve  unite  with  the 
twelve  within  the  ovum,  reduced  from  i'zventy-four,  to  form 
the  twenty-four  found  in  all  cells  that  are  derived  from  the 
segmenting  ovum. 

In  the  formation  of  spermatozoa,  the  spermatids  are  of 
the  most  importance.  According  to  some  authors,  the  nucleus 
forms  the  whole  organism,  w^hile  others  hold  the  head  and 
middle-piece  are  of  nuclear  origin,  and  the  tail  protoplasmic. 
These  cells  become  crowded  or  drawn  to  the  columns  of  Ser- 
toli, to  which  they  apparently  attach  themselves.  At  the 
same  time,  the  shape  of  the  cell  becomes  modified  by  elonga- 
tion.   The  CHROMATIN  of  the  nucleus  becomes  denser,  and 


I 


SPERMATOGENESIS.  175 

migrates  toward  the  attached,  or  peripheral  end,  while  the 
protoplasm  draws  toward  the  central  end.  At  the  attached, 
or  peripheral,  end,  the  nucleus  has  a  small  prominence  de- 
veloped that  indicates  the  future  head.  The  protoplasm  be- 
comes clear  and  draws  centrally,  forming  a  slender  vesicle,  in 
the  middle  of  which,  a  delicate  line  appears.  This  line  joins 
the  head,  and,  growing  backward,  breaks  through  the  mem- 
brane to  form  the  tail  of  the  spermatozoon. 

The  CENTROSOMES,  usually  two  in  number,  become  differ- 
ent in  shape ;  the  smaller  becomes  rod-like,  and  passes  to  the 
head  of  the  spermatozoon  to  become  the  acrosome.  The 
larger  is  cone-shaped,  and  differentiates  into  two  portions, 
the  largest  of  which  passes  toward  the  nucleus,  and  develops 
a  globular  extremity,  the  end-knob.  This  unites  peripheral- 
ly with  the  nucleus,  and  elongates  centrally  to  become  the 
middle-piece;  the  smaller  part  elongates  to  form  the  axial 
fibre.    The  envelop  is  held  to  be  protoplasmic  in  origin. 

As  the  spermatozoa  continue  to  develop,  the  column  of 
Sertoli  increases  in  length,  and  when  development  is  com- 
plete, the  organisms  lie  in  the  lumen  of  the  tubule.  The 
column  of  Sertoli,  with  the  attached  spermatids,  is  called  a 

SPERMATOBLAST. 

The  Semen  consists  principally  of  spermatozoa  suspended 
in  a  fluid  derived  from  the  various  portions  of  the  genital 
tract.  The  spermiatozoa  are  practically  amotile  until  mixed 
with  the  secretion  of  the  prostate,  when  they  become  actively 
motile.  Beside  the  prostatic  fluid,  other  secretion  is  added 
by  the  seminal  vesicles,  glands  of  Cowper  and  urethral  glands 
(Littre).  In  addition  to  the  spermatozoa,  crystals  and  amy- 
loid bodies  from  the  prostate,  fat  globules  and  epithelial  cells 
are  seen  in  the  semen. 

Motility  may  be  exhibited  by  the  spermatozoa  twenty- 
four  hours  after  death.     They  have  been  kept  alive  for  two 


176  THE    MALE  GENITAL   SYSTEM. 

weeks,  under  proper  conditions,  and  this  may  readily  occur 
in  the  female  genital  tract.  Water,  acids  and  metallic  salts 
cause  cessation  of  action,  while  alkaline  and  normal  salt 
solutions  aid  it.  It  seems,  from  experiment,  that  they  travel 
better  against  than  with  the  current. 

The  Vas  Deferens  connects  the  testicle  with  the  urethra. 
It  passes  into  the  body  through  the  inguinal  canal,  and  is  ac- 


FiG.  66. — Human  SrERMATOzoA. 

1.   Surface  view  ;  2.  s'de  view  :  3,  looped  seminal  filament ;  4.  spermatozoan 
of  an  ox ;  a.  head  ;  h.  middle  piece  ;  c.  tail. 


companied,  to  the  internal  ring,  by  the  spermatic  artery  and 
vein,  the  gubernaculum  testis  (muscle  tissue)  and  fibrous 
connective  tissue.    This  forms  the  spermatic  cord. 

THE  VAS  DEFERENS. 

The  Vas  has  three  coats,  mucous,  muscular  and  fibrous. 

The  mucous  coat  consists  of  stra Med  columnar  cells  rest- 
ing upon  basement  membrane  and  tunica  propria.  It  is  usu- 
ally thrown  into  longitudinal  folds.  The  cells  in  the  first 
portion  may  be  stratified  ciliated  continued  from  the  epi- 
didymis. 

The  muscular  coat  is  composed  of  smooth  muscle  tissue 
usually  arranged  as  inner  and  outer  longitudinal  and  middle 


SEMINAL   VESICLES   AND    PROSTATE.  1 77 

circular  layers.    These  are  not  always  distinct,  as  they  may 
interlace,  more  or  less. 

The  FIBROUS  coat  consists  of  fibro-elastic  tissue,  and  gives 
strength  to  the  organ. 

THE  SEMINAL  VESICLES. 

The  Seminal  Vesicles  lie  beneath  the  bladder,  and  enipty 
into  the  vas  through  the  seminal  ducts.  They  consist  of 
three  coats,  mucous,  muscular  and  fibrous. 

The  MUCOUS  coat  is  lined  by  simple  columnar,  or  pseudo- 
^tratiiied,  cells  that  possess  yellow  pigment  granules.  These 
cells  rest  upon  basement  micmbrane  and  tunica  propria.  The 
whole  coat  is  thrown  into  waves,  or  folds,  to  which  an  ap- 
parent stratification  of  the  cells  is  due. 

Th^  muscular  coat  consists  of  inner  circular  and  outer 
longitudinal  layers  of  the  smooth  variety. 

The  FIBROUS  coat  is  indistinct. 

These  organs  act  as  reservoirs  for  spermatozoa,  at  times, 
beside  secreting  a  fluid  that  helps  to  make  up  the  semen. 

The  Ejaculatory  Ducts  are,  in  reality,  the  continuation  of 
the  vas.  They  are  lined  by  simple  columnar  cells,  like  the 
seminal  vesicles.  The  muscle  tissue  is  chiefly  longitudinally 
arranged. 

THE  PROSTATE. 

The  Prostate  is  a  compound  tubular  gland.  It  is  sur- 
rounded by  a  CAPSULE^  and  is  composed  of  three  main  lobes. 
The  CAPSULE  consists,  externally,  of  a  thin  layer  of  white 
fibrous  tissue,  beneath  which  is  a  thick  layer  of  smooth 
muscle  tissue.  From  the  latter,  trabeculae  pass  into  the 
center  of  the  organ,  and  converge  at  the  urethra.  They  pos- 
sess thick  bases,  but  taper  as  the  center  is  approached.  These 
partitions  form  compartments  in  which  the  glands  are 
found. 


178 


THE    MALE   GENITAL    SYSTEM. 


The  GLANDS  are  of  the  branched  tubular  variety,  and  the 
ALVEOLI,  or  SECRETORY,  PORTIONS  are  lined  by  simple  colum- 
nar cells,  and  are  separated  from  one  another  by  the  muscu- 
lar trabecidae.  The  basal  portions  of  the  cells  contain  gran- 
ules that  have  an  affinity  for  the  acid  stains.    The  ducts  are 


'<?? 


^*-4 


if;/ 


^*^^, 


/ 


Fig.  67. — Section  of  the  Prostate  Gland. 

a.  Interstitial  tissue  and  muscular  trabecula  :  ft.  capsule  ;  c.  glands;  d.  pro- 
static bodies ;  e.  secretion  ;  f.  blood-vessel ;  g.  duct. 


a  dozen  or  so  in  number,  and  are  lined  by  simple  columnar 
cells,  except  at  their  outer  ends,  where  transitional  cells  of  the 
urethra  are  found.  These  ducts  empty  into  the  floor  of  the 
urethra.  The  alveoli  contain  a  varying  number  of  bodies 
which  are  few  in  youth  and  numerous  in  old  age. 


PENIS.  179 

The  vessels  that  supply  the  tubules,  ramify  in  the  muscular 
septa,  and  form  plexuses  of  capillaries  that  surround  the 
tubules.  The  veins  run  toward  the  periphery,  and  form  a 
network  in  the  capsule. 

The  lymphatics  originate  in  the  septa,  and  follow  the  ves- 
sels. 

Nerve  fibres  are  numerous,  and  some  special  sensory  end- 
ings are  present. 

The  Glands  of  Cowper  are  racemose  glands  that  open 
into  the  membranous  portion  of  the  urethra.  They  are 
surrounded  by  a  capsule  of  white  fibrous  tissue  that  divides 
the  gland  into  lobes  and  lobules.  The  alveoli  that  make  up 
a  lobule  are  lined  hy  low  columnar  mucous  cells.  These  rest 
upon  basement  membrane  and  tunica  propria.  The  smaller 
ducts  are  lined  by  cuboidal  cells,  while  the  larger  possess 
stratified  columnar  cells.  Bundles  of  muscle  fibres  are 
present. 

THE  PENIS. 

The  Penis  is  a  peculiar  organ  surrounded  by  a  loosely 
attached  skin.  The  latter  contains  no  adipose  tissue.  The 
skin  extends  over  the  end  of  the  organ  as  the  prepuce,  which 
is  covered,  upon  both  surfaces,  by  stratified  squamous  cells. 
The  inner  surface  possesses  the  characteristics  of  a  mucous 
membrane. 

The  organ  consists  of  two  main  portions,  the  glans  and 
the  body. 

The  glans  is  covered  by  stratified  squamous  cells,  and  is 
separated  from  the  body  by  a  narrow  constricted  area,  the 
CERVIX.  At  this  point,  the  squamous  cells  of  prepuce  and 
glans  are  continuous. 

The  body  consists  of  tzi^o  corpora  cavernosa  and  the 
single  corpus  spongiosum. 


.  l8o  THE    MALE  GENITAL    SYSTEM. 

The  CORPORA  CAVERNOSA  He  side  by  side,  forming  the 
dorsal  portion  of  the  penis,  and  are  bound  together  by  a 
thick  sheath  of  white  fibrous  tissue  called  the  tunica  albu- 
ginea.  From  the  inner  surface  of  this,  trabeculae  pass  in- 
ward and  form  a  series  of  communicating  spaces,  or  caverns. 
These  are  venous  blood  spaces.  The  trabeculae  contain  tor- 
tuous arteries,  the  helicine  arteries,  which,  when  engorged, 
become  straightened  as  the  organ  increases  in  size.  The 
spaces  become  filled  with  blood,  and,  with  the  vascular 
trabeculae,  constitute  true  erectile  tissue.  This  engorgment 
produces  the  erection.  False  erectile  tissue  depends  for  its 
action  upon  smooth  muscle  tissue. 

The  CORPUS  SPONGIOSUM  has  a  thin  tunic,  and  consists  of 
two  portions,  urethral  and  peripheral.  The  urethral  part  is 
quite  dense  and  rich  in  veins,  while  the  peripheral  part  re- 
sembles, somewhat,  the  cavernous  portion. 

The  glans  is  a  continuation  of  the  corpus  spongiosum, 
and  consists  of  a  delicate  network  of  connective  tissue  en- 
closing a  number  of  small  spaces.  It  is  covered  by  a  delicate 
skin,  which  is  continuous  with  the  prepuce,  or  foreskin.  In 
the  cervix  are  located  a  number  of  glands  that  secrete  the 
smegma.  These  are  the  glands  of  Tyson,  or  glandulae 
oderi ferae. 

The  blood-vessels  and  spaces  are  numerous.  The  arterial 
branches  follow  the  septa,  in  which  they  run  such  a  convo- 
luted course  as  to  receive  the  name  of  helicine  arteries.  They 
form  capillary  plexuses  in  the  trabeculae,  some  of  which 
empty  into  the  spaces,  while  others  pass  over  into  the  veins. 
The  branches  within  the  tunica  form  capillaries  that  empty 
into  the  spaces.  Anastomoses  between  arterial  and  venous 
capillaries  are  numerous. 

The  emissary  veins  receive  blood  from  the  tunica  and 
superficial  vessels,  and  partly  from  the  deeper  tissues  and 


PARADIDYMIS.  l8l 

vessels ;  they  pass  through  the  tunica  to  empty  into  the  dorsal 
vein  of  the  penis  that  lies  in  a  groove  between  the  corpora 
cavernosa.  These  veins  are  pressed  upon  when  the  super- 
ficial vessels  are  filled  with  blood,  in  that  way  preventing 
egress  but  not  ingress. 

Nerve  endings  include  corpuscles  of  Meissner,  end-bulbs, 
genital  corpuscles,  Pacinian  bodies  and  intra-epithelial  free 
endings. 

The  Paradidymis,  or  organ  of  Giraldes>  is  found  in  the 
epididymis.  It  consists  of  a  number  of  tubules,  in  which  the 
lining  cells  are  low  columnar,  or  even  ciliated.  The  tubules 
are  closed,  and  are  separated  from  one  another  by  vascular 
connective  tissue. 

The  cells  that  line  the  various  portions  of  the  male  genital 
tract  are  as  follows : 

Testicle. 

'Spermatogonia      )  ^ 
c,     ^     ,       1  y  Basal  layer. 

Sustentacular         j 

Seminiferous  Tubule \  Spermatocytes,  or  mother  cells. 

Second  layer. 
Daughter  cells,  Third  layer. 
.Spermatids,  Fourth  layer. 

TuBULi    Recti Cuboidal  or  squamous, 

Rete  Testis Cuboidal  or  squamous. 

Vasa  Efferentia Columnar  or  ciliated. 

Epidydimis Stratified  ciliated. 

Stratified  columnar. 
Stratified  ciliated  (some). 

Seminal  Vesicles Simple  or  pseudositratified  columnar. 

Ejaculatory  Duct Simple  columnar. 


Vas  Deferens I 

\ 


CHAPTER  XIV. 


THE  FEMALE  GENITAL  SYSTEM. 

This  system  consists  of  the  Ovary,  Oviduct,  Uterus, 
Vagina,  Glands  of  Bartholin  and  Genitalia. 

The  Ovary,  the  distinctive  female  organ,  Hes  upon  the 
posterior  surface  of  the  broad  Hgament  and  projects  into  the 
pelvic  cavity.  It  is  surrounded  by  a  capsule  of  white  fibrous 
connective  tissue  called  the  tunica  albuginea.  This  is  not 
so  prominent  as  that  of  the  testicle.  The  free  surface  of 
the   capsule   is    covered  by   low    columnar    cells    called   the 

GERMINAL  EPITHELIUM. 

The  organ  consists  of  Cortex  and  Medulla. 

The  Cortex  is  the  outer  part,  and  surrounds  the  medulla, 
except  at  one  point,  at  which  the  vessels  enter  and  leave ;  this 
is  the  HiLUM,  and  here  the  medulla  comes  to  the  surface. 
The  cortex  is  the  glandular  portion,  where  the  cellular  ele- 
ments of  the  secretion,  the  ova,  are  formed.  It  consists  of 
a  delicate  reticulum,  the  stroma,  in  which  the  Graafian 
FOLLICLES  are  found,  and  occasionally  groups  of  large, 
polygonal  epithelial  cells,  called  the  interstitial  cells. 
The  free  surface  of  the  stroma  is  covered  by  the  modified 
mesothelial  cells,  the  germinal  epithelium,  from  which 
the  ova  are  derived.    These  cells  are  low  columnar  elements. 

The  Graafian  follicles  are  characteristic  structures.  They 
vary  in  size;  the  smallest  are  just  beneath  the  tunica  albu- 
ginea, the  medium-sized  near  the  medulla,  and  the  largest 
extend  from  the  medulla  to  the  capsule,  and  cause  a  projec- 
tion upon  the  surface  of  the  organ. 

Externally  the  follicle  is  covered  by  a  layer  of  condensed 
stroma  called  the  thecaj^olliculi  ;  the  outer  portion  of  this 
is  called  the  tunica  fibros.\,  and  the  inner  the  tunica  vas- 

'182  ^^^      "^        ' 


OVARY. 


183 


CULOSA.  The  THECA  is  lined  by  a  number  of  layers  of  gran- 
UTarcells  termed  the  zona  c.ranulqsAi^  within  which  is  a 
space,  the  antrum,  filled  by  a  liquid,  the  ljouor  folliculi. 
At  one  point,  the  granule  layer  projects  into  the  antrum, 
and  this  mass  contains  the  ovum.    This  projection  is  called 


I 


Big.  68. — Cross-section  of  Ovary  op  a  Cat. 
The  Graafian  follicles  are  so  numerous  that  but   little  of  the   medulla 
is  seen. 

a.  Germinal  epithelium ;  h.  tunica  albuginea ;  c.  immature  Graafian  fol- 
licle:  d.  ovum;  e.  cortical  stroma:  f.  interstitial  cells;  (j.  theca  fol- 
liculi ;  h.  zona  granulosa ;  i.  antrum  containing  liquor  folliculi  ;  k. 
discus  proligerus  :  I.  corona  radiata  :  m.  zona  pellucida ;  n.  vitellus: 
o.  germinal  vesicle ;  p.  follicle  without  ovum  ;  r.  hilum  ;  s.  medulla 
showing  the  tubules  of  the  parovarium  ;  t.  arteriole  ;  u.  venule. 

the  DISCUS  PROLIGERUS,  or  CUMULUS  oviGERUs.  Just  withiu 
the  granule  cells  ot  the  discus  is  seen  a  layer  of  long  columnar 
cells,  the  corona  radiata.  These  cells  rest  upon  a  thick 
homogeneous  membrane  called  the  zona  pellucida,  which 
is  separated   from  the  ovum  by  a  small  space,  called  the 


184  THE   FEMALE   GENITAL   SYSTEM. 

PERiviTELLiNE  SPACE.  This  Space  is  disputed  by  some 
writers.  The  corona  is  supposed  to  give  rise  to  the  zona  pel- 
lucida.  The  ovum  that  Hes  just  within  the  space  consists 
of  a  cell-wall,  the  vitelline  membrane,  and  cell-body,  the 
viTELLUS.  In  the  vitellus  is  seen  the  nucleus,  or  germinal 
VESICLE,  which  contains  the  prominent  nucleolus,  or  germi- 
nal  SPOT. 

The  Ovum  is  the  most  characteristic  and  largest  cell  in 
the  body.  Its  diameter  varies  from  .2  to  .3  mm.  The  zona 
pellucida  that  surrounds  it  is  quite  thick,  measuring  from 
7  to  10  microns.  The  protoplasm  consists  of  yolk  granules, 
the  nutritive  yolk,  or  deutoplasm,  and  the  formative 
YOLK.  The  nucleus  averages  about  30  microns,  is  eccen- 
trically placed  and  sharply  outlined  by  a  membrane  that  pos- 
sesses a  double  contour.  The  chromatin  is  rather  scant,  but 
the  nucleolus  is  quite  large  and  prominent. 

The  Graafian  follicles,  of  which  there  are  about  36,000 
in  each  ovary,  are  developed  during  intrauterine  life,  and 
all  are  usually  present  at  birth.  Not  all  of  these  develop, 
by  any  means.  The  smallest  consist  of  the  ovum^ 
surrounded  closely  by  a  few  layers  of  small  granule 
cells  and  a  delicate  theca.  They  lie  just  beneath 
the  tunica  albuginea,  and  show  no  antrum.  The 
medium-sized  follicles  lie  near  the  medulla,  and  pre- 
sent an  antrum.  The  granule  cells  are  more 
numerous,  and  the  ovum  larger.  The  fully-developed  fol- 
licles extend  from  the  medulla  through  the  cortex  beyond 
the  original  surface  level,  projecting  varying  distances. 

The  FOLLICULAR  CELLs_are  derived  from  the  germinal  epi- 
thelium, and  grow  into  the  stroma  in  long  columns  during 
the  developmental  period,  as  the  egg-tubes  of  PfluegeRj^ 
In     such     a     column,     will     be     found     several     large, 
and  a  great  number  of  small,  cells.    These  columns  become 


OVARY. 


185 


separated  into  a  number  of  groups  of  cells  consisting  of  one 
or  more  large,  and  many  small,  cells.  The  large  are  the 
OOGENETIC^  and  the  small  the  granule,  cells.  Gradually, 
the  large  cells  fuse  to  form  a  single  mass  of  protoplasm,  and 
all  the  nuclei,  except  one,  disintegrate.  The  single  cell  re- 
sulting is  called  the  oocyte.  The  egg-tubes  are  separated 
into  these  groups  by  the  stroma  that  grows  into  the  columns. 


'^■<^^m^ 


Fig.  69. — Ovum  from  a  Cow. 

1.  Corona   radiata ;    2.   zona  pellucida ;    3.   vitellus ;    4.   germinal   vesicle ; 
5.  germinal  spot. 


I 


This  stroma  further  condenses  around  each  group  to  form 
the  primitive  theca.  Toward  the  age  of  puberty,  these 
follicles  begin  to  develop,  though  they  may  start  sooner. 
The  granule  cells  increase  rapidly  in  number,  and  some  of 
the  more  central  ones  (iisappear  by  disintegration  or  lique- 
faction. This  gives  rise  to  the  space,  or  antrum,  which  be- 
comes filled  by  a  liquid,  the  liquor  folliculi.  The  latter 
is  probably  derived  from  the  blood-vessels. 


l: 


l86  THE   FEMALE   GENITAL   SYSTEM. 

As  the  follicle  develops  and  is  about  to  rupture,  the  ovum 
(oocyte)  undergoes  a  process  called  Maturation. 

Maturation  is  the  process  by  which  the  polar  bodies  are 
formed  and  extruded.  The  germinal  vesicle  migrates  toward 
the  periphery,  and  undergoes  mitotic  change.  When  the 
nuclear  spindle  is  formed  parallel  to  one  of  the 
radii,  the  peripheral  half^  surrounded  by  a  small 
amount  of  protoplasm,  is  thrust  out  of  the  cell. 
This  is  the  first  polar  body.  Without  rest,  the 
remaining  chromosomes  immediately  undergo  division 
again,  and  the  extrusion  process  is  repeated.  This  is  the 
second  polar  body.  The  remaining  chromosomes  form  a 
new  nucleus  called  the  germ-nucleus.  By  this  change,  the 
number  of  chromosomes  is  reduced  from  twenty-four,  in 
the  oocyte,  to  twelve,  in  the  matured  ovum.  The  first  polar 
body  often  divides  into  two,  and  as  a  result  of  maturation, 
four  cells  are  formed.  Of  these  four,  the  ovum  is  the  only 
one  capable  of  producing  an  offspring.  The  three  polar 
bodies  disintegrate  and  disappear.  This  is  entirely  different 
from  the  change  in  the  testicle.  In  that  organ,  the  sperma- 
tocyte gives  rise  to  four  cells,  each  of  which  becomes  a 
spermatozoon,  capable  of  fertilization. 

As  the  follicle  increases  in  size,  it  approaches  the  tunica 
albuginea,  and  causes  it  to  protrude.  The  stroma  interven- 
ing between  the  ovum  and  the  tunica  gradually  diminishes 
until  merely  the  tunica  remains.  As  the  follicle  increases, 
and  the  pressure  within  becomes  greater,  the  tunica  becomes 
progressively  thinner,  until  it  is  no  longer  able  to  withstand 
the  pressure.  Then  it  ruptures,  and  the  liquor  folliculi  and 
the  ovum,  surrounded  by  the  granule  cells,  are  cast  out  of 
the  ovary.  The  vessels  of  the  tunica  vasculosa  rupture,  and 
the  follicle  fills  with  blood.  When  this  occurs,  the  body  is 
called  the  corpus  hemorrhagicum.  _The  cells  of  the  theca 
penetrate  the  clot,  and  cause  this  to  organize.     In  addition 


OVULATION.  187 

to  these  cells,  there  are  certain  other  large  cells  that  possess 
a  yellowish  pigment.  These  are  the  lutein  cells,  and  their 
function  is  unknown.     They  are  derived  from  the  theca. 

If  the  ovum  has  not  been  fertilized,  this  body  is  called  a 
CORPUS  LUTEUM  SPURIUM^ which  rapidly  undergoes  atrophy; 
in  a  few  weeks,  it  leaves  a  white  scar  called  the  corpus  albi- 
cans^ If  fertilization  has  occurred,  then  the  body  persists 
until  near  the  end  of  pregnancy,  and  is  termed  the  corpus 

LUTEUM_\^ERUM. 

The  corpus  luteum  seems  to  be  a  gland  of  short  duration. 
It  seems  to  secrete  a  substance  that  causes  the  second  suc- 
ceeding menstrual  How.  Experimental  study  upon  animals, 
in  which  the  follicles  were  destroyed,  showed  an  almost  in- 
variable absence  of  the  second  succeeding  period.  The  pre- 
ceding flow  was  caused  by  the  follicle  preceding  the  experi- 
ment. This  secretion  also  stimulates  the  uterus,  and  aids 
the  implantation  of  the  ovum  in  the  uterine  mucosa,  provid- 
ing fertilization  has  occurred.     (Frankel). 

Of  all  the  follicles  formed,  but  few  are  ever  fertilized.  A 
great  number  atrophy;  in  the  remiainder,  maturation  oc- 
curs. Of  these  ova,  there  are  those  which  are  cast  into  the 
abdominal  cavity  and  absorbed  by  the  peritoneum;  those  in 
which  the  ovum  passes  down  the  genital  tract  and  is  cast 
out,  or  disintegrates,  and  lastly,  those  that  become  fertilized. 

Ovulation  includes  the  delivery  of  the  ovum  from  the 
follicle  and  its  passage  through  the  genital  apparatus.  In 
the  lower  animals,  in  which  the  young  are  developed  from 
eggs  outside  of  the  body  (oviparous),  this  process  is 
evinced  by  the  'laying  of  the  egg"  In  the  viviparous  ani- 
mals, or  those  in  which  the  offspring  is  developed  within 
the  mother,  this  process  is  not  accompanied  by  any  outward 
signs  or  manifestations.  In  the  temperate  climate,  it  begins 
at  about  the  twelfth  to  the  fifteenth  year,  and  continues  until 


l88  THE   FEMALE   GENITAL   SYSTEM. 

about  the  forty-fifth  to  the  fiftieth  year.  At  that  time  it 
ceases,  and  fertihzatioii  cannot  occur  thereafter. 

The  Medulla  consists  of  a  loose  network  formed  by  large, 
coarse  bundles  of  white  fibrous  tissue,  in  which  strands  of 
SMoaTH  MUSCLE  TISSUE  are  found.  These  latter  are  limited 
to  the  medulla.  In  the  meshes  of  the  stroma  are  seen  the 
INTERSTITIAL  CELLS^  which  are  more  numerous  than  in  the 
cortex.  In  this  part  of  the  ovary  are  found  the  large  blood- 
vessel trunks,  which  are  very  numerous. 

The  vessels  enter  the  ovary  at  the  hilus,  and  fonn  a  large 
number  of  branches  in  the  medulla.  From  these,  smaller 
ones  are  sent  to  the  corte:^:,  some  passing  to  the  follicles, 
where  they  form  a  dense  surrounding  plexus,  while  others 
pass  to  the  tunica  vasculosa  of  the  tunica  albuginea. 

The  lymphatics  follow  the  vessels  closely. 

Nerve  fibres  accompany  the  vessels,  and  surround  the 
follicles.     Ganglia  occur  in  the  medulla. 

The  Parovarium,  or  Epoophoron,  lies  near  the  hilus  of 
the  ovary,  and  consists  of  a  number  of  short  vertical  tubules 
united  to  a  single  horizontal  tube.  The  vertical  tubules  are 
short,  and  are  lined  by  low  columnar  cells.  The  horizontal 
tubule  has  a  larger  diameter  than  the  preceding,  and  is  lined 
by  the  same  variety  of  cells.  It  often  lies  deep  in  the  broad 
ligament. 

The  Paroophoron  lies  in  the  broad  ligament,  between 
the  ovary  and  uterus,  and  consists  of  a  number  of  short, 
closed  tubules  lined  by  low  columnar  cells.  The  tubes  re- 
semble the  vertical  tubes  of  the  epoophoron. 

THE  FALLOPIAN  TUBE. 

Although  the  ovary  possesses  no  excretory  apparatus  like 
other  glands,  the  Oviduct,  or  Fallopian  Tube,  acts  as  such. 

The  Fallopian  Tube  consists  of  the  outer  fimbriated 
END,  the  middle,  or  ampulla,  and  the  inner  uterine  end,  or 


FALLOPIAN  TUBE. 


189 


ISTHMUS.      It    has    three    coats,    mucous,    muscular    and 

FIBROUS. 

The  mucous  coat  consists  of  simple  ciliated  cells  that  lie 
upon  a  basement  membrane  and  tunica  propria.  A  muscii- 
laris  mucosae  is  absent.     The  tunica  propria  is  thrown  into 


Fig.    70. — Cross-section    of    the    Human    Fallopian    Tube. 

a.  Epithelium  ;  h.  tunica  propria  :  c,  villi ;  d.  muscular  coat,  inner  circular 
layer ;  e.  muscular  coat,  outer  longitudinal  layer ;  f.  blood-vessels  in 
the  fibrous  coat ;  g.  blood-vessels  in  villus ;  h.  fibrous  coat ;  k.  epi- 
thelium of  fimbria ;  I.  tunica  propria  of  fimbria. 


longitudinal  folds  that  are  high  in  the  fimbriated  end,  but 
diminish  in  heighth  as  the  uterus  is  approached.  These 
folds  are  the^iLLi,  which  possess  a  very  narrow  base,  but 
the  part  lying  in  the  lumen  of  the  tube  is  greatly  branched. 
The  tunica  propria  consists  of  white  fibrous  and  yellow 
elastic  tissues,  in  which  diffuse  adenoid  tissue  is  found. 


190  THE    FEMALE   GENITAL    SYSTEM. 

The  MUSCULAR  coat  consists  of  involuntary  nonstriated 
muscle  tissue  arranged  in  inner  circular  and  outer  longitudi- 
nal layerj.  Near  the  uterine  end,  an  inner  longitudinal  layer 
is  added.     This  corresponds  to  a  muscularis  mucosae. 

The  FIBROUS  coat  consists  of  white  fibrous  tissue,  and  is 
surrounded  by  peritoneum. 

The  blood-vessels  lie  in  the  deeper  portion  of  the  tunica 
propria.  From  these,  smaller  ones  are  sent  into  the  villi, 
and  into  the  muscular  and  fibrous  coats.  The  vessels  are 
usually  quite  tortuous. 

The  lymphatics  accompany  the  blood-vessels. 

The  nerves  are  both  medulla-ted  and  nonmedullated.  They 
accompany  the  blood-vessels,  which  they  supply,  and  then 
pass  to  the  mucosa,  where  they  end  in  relation  with  the 
cells. 

THE  UTERUS. 

The  Uterus  is  a  flattened,  pear-shaped  organ  that  con- 
sists of  BODY  and  cervix.  It  is  an  important  organ,  as  within 
it  develops  the  offspring,  in  viviparous  animals.  All  parts 
consist  of  MUCOUS,  muscular  and  fibrous  coats. 

The  MUCOUS  coat  of  the  body  is  about  i  mm.  in  thickness, 
and  is  composed  of  simple  ciliated  cells,  basement  mem- 
brane and  tunica  propria.  Within  the  latter  are  found  a 
rich  capillary  plexus  and  diffuse  lymphoid  tissue.  The  sur- 
face is  not  smooth,  but  is  broken  by  the  formation  of 
GLANDS.  These  are  tube-like  depressions  lined  by  the  simple 
ciliated  cells,  and  are  of  the  branched  tubular  variety.  They 
are  the  uterine  glands  and  extend  to  the  muscular  coat, 
but  do  not  penetrate  it.  They  are  often  so  long,  that,  when 
they  reach  the  muscular  coat,  they  turn  and  run  parallel  to 
it  for  some  distance. 

The  MUCOSA  of  the  cervix  is  a  little  different.  The  uter- 
ine end  is  lined  by  simple  ciliated  cells,  and  glands  are  pres- 


UTERUS. 


191 


ent.  The  vaginal  end  is  lined  by  stratified  squamous  cells, 
and  gland-like  depressions  are  present.  The  orifices  often 
close,  causing  them  to  become  distended  with  secretion.  In 
this  condition,  they  produce  globular  projections  called  the 
ovuLi  Nabothi.     The  cervical  mucosa  is  thrown  into  folds 


iS^^SSis^^^^^^D 


Fig.    71. — Resting   Uterine    Mucosa. 
a.  Mucosa ;    b.    epithelium ;     c.    gland    tubule     {Stohr's    Histology,    after 
Bohm  and  Davidoff). 

called  the  plicae  palmatae.     The  vaginal  portion  of  the 
cervix  is  covered  by  stratified  squamous  cells. 
H|      The  MUSCULAR  coat  consists  of  three  layers  of  smooth 
^"  muscle,  inner  longitudinal,  middle  circular  and  outer  longi- 
tudinal   The  inner  longitudinal  represents  an  hypertrophied 


192  THE   FEMALE   GENITAL   SYSTEM. 

muscuiarts  mucosae.  It  is- separated  from  the  middle  layer 
by  a  very  thin  layer  of  connective  tissue.  This  muscle  layer 
is  called  the  stratum  mucosum.  The  middle  layer  is  the 
thickest,  and  contains  the  large  vessels.  It  is  called  the 
stratum  vasculare.  The  outer  longitudinal  layer  lies  just 
beneath  the  fibrous  coat,  and  is  often  called  the  stratum 

SUPRA  vasculare.  _ 

In  the  CERVIX,  the  circular  fibres  are  more  pronounced, 
forming  a  dense  band  or  ring. 

The  muscle  fibres  average  50  to  60  microns  in  length ; 
but,  during  pregnancy,  they  lengthen  to  from  300  to  600 
microns. 

The  FIBROUS,  or  serous,  coat  is  quite  thin.  It  is  com- 
pletely invested  by  peritoneum  in  the  body. 

Menstruation  is  the  periodic  change  that  occurs  in  the 
uterine  mucosa,  every  twenty-eight  days,  during  the  child- 
bearing  period  (13th  to  50th  year).    It  is  divided  into  stages, 

the  HYPERTROPHIC,  DESQUAMATIVE,  REPARATIVE  and  RESTING 

stages. 

During  the  hypertrophic,  or  constructive  stage,  the 
mucosa  increases  to  2  or  3  mm.  in  thickness,  and  the  surface 
becomes  irregular.  This  is  due  to  the  increase  in  size  and 
number  of  the  blood-vessels,  and  to  cell  proliferation  in  the 
tunica  propria.  The  glands  become  broader,  deeper  and 
more  tortuous.  This  change  requires  four  to  six  days,  and 
is  succeeded  by  the  desquamative,  or  destructive  stage. 

The  DESQUAMATIVE,  or  DESTRUCTIVE,  Stage  is  characterized 
by  the  appearance  of  the  flow,  or  flux.  It  is  caused  by 
the  diapedesis  of  some  of  the  blood  from  the  capillaries  of 
the  tunica  propria.  The  blood  passes  into  this  layer  be- 
neath the  epithelium,  and  cuts  ofT  the  nutrition  of  the  over- 
lying cells,  causing  them  to  undergo  a  fatty  degeneration. 
These  cells  then  disintegrate,  exposing  the  vessels,   which 


VAGINA.  193 

rupture  and  allow  the  blood  to  pass  into  the  uterine  cavity. 
The  surface  is  thus  left  without  an  epithelial  covering,  and 
the  thickness  of  the  mucosa  becomes  reduced.  This  stage, 
lasting  three  to  five  days,  is  followed  by  repair. 

The  REPARATIVE  Stage  is  that  in  which  the  mucosa  re- 
turns to  the  normal  condition.  The  hyperemia  disappears, 
and  the  disintegrated  epithelium  is  replaced  by  epithelial 
cells  from  the  glands.  This  stage  requires  about  five  to 
eight  days. 

The  RESTING  stage  constitutes  the  remaining  twelve  to 
fourteen  days  of  the  period.  During  this  stage,  the  uterine 
mucosa  is  quiescent.  Should  fertilization  occur  at  the  time 
of  the  constructive  stage,  the  other  three  stages  may  not  take 
place. 

The  blood-vessels  are  important.  Two  arteries,  the  uter- 
ine and  ovarian,  supply  the  organ.  The^  main  branches  of 
these^  arteries  pass  to  th^  middle  circular  layer  of  rnuscle,- 
which  plays  the  part  of  submucosa.  Smaller  branches  are 
sent  into  the  mucosa,  and  there  form  plexuses  around  the 
glands.  The  large  trunks  are  very  tortuous,  to  allow  for  the 
increase  in  the  size  of  the  uterus  during  pregnancy. 

The  lymphatics  originate  in  the  mucosa;  these  vessels 
empty  into  a  set  of  larger  vessels  in  the  middle  layer  of  the 
muscular  coat.  From  here,  the  vessels  pass  into  the  serous 
coat. 

The  nerve  Hhres  are  both  medullated  and  nonmedullated. 
The  former  pass  into  the  mucosa,  some  ending  in  the  epi- 
thelial layer.    The  latter  pass  chiefly  to  the  muscular  tissue. 

THE  VAGINA. 

The  coats  of  the  Vagina  are  the  same  as  those  of  the 
uterus. 

The  MUCOUS  coat  consists  of  stratified  squamous  cells, 
supported  by  a  basement  membrane  and  tunica  propria.   The 


194 


THE   FEMALE   GENITAL   SYSTEM. 


subepithelial  portion  of  the  tunica  propria  is  papillated.  Tht* 
deeper  portion  contains  many  large  elastic  fibres  and  con- 
siderable diffuse  lymphoid  tissue.    Occasionally,  some  simple 


-^-  'lpwim'^%mi^-^ji^^v'm:m^m^i 


Fig.   72. — Cross-section   of    Segment   of   Human   Vagina. 
a.    Stratiflecl    squamous   epithelium:    h.   tunica   propria;    c.    inner    circular 
muscle  fibres  ;  d    outer  mixed  muscle  fibres. 

tubular  glands  are  met  with,  and  the  lining  cells  arc  of  ihi 
simple  ciliated  variety. 

The  MUSCULAR  coat  varies  in  thickness,  that  nearer  the 
outlet  being  the  thicker.  The  layers  are  not  shari;ly  separ- 
ated from  one  another,  but  the  general  direction  is  inner  cir- 


GENITALIA  I9S 

cular  and  outer  longitudinal  The  mucous  and  muscular 
coats  are  thrown  into  folds  that  are  called  rugae. 

The  FIBROUS  coat  consists  of  dense  fibrous  tissue,  and 
serves  to  connect  the  vagina  with  the  surrounding  tissues 
and  organs. 

The  larger  vessels  lie  in  the  deeper  portion  of  the  mucosa, 
and  send  branches  into  the  mucosa  and  muscularis.  The 
capillaries  of  the  mucosa  pass  chiefly  to  the  papillae.  The 
veins  form  dense  plexuses  beneath  the  fibrous  coat.  Large 
vessels  occur  in  the  lower  part  of  the  mucosa,  causing  it  to 
resemble  cavernous  tissue. 

The  lymphatics  follow  the  same  course  as  the  blood- 
vessels. 

The  nerves  are  both  nonmedullated  and  medullated.  Geni- 
tal corpuscles  may  be  found  in  the  mucosa. 

THE  GENITALIA. 

The  VAGINAL  ORIFICE  is  guarded  by  a  delicate  annular,  or 
crescentic  membrane  called  the  Hymen.  This  consists  of 
white  fibrous  tissue  covered  upon  its  external  and  internal 
surfaces  by  stratified  squamous  cells.  Occasionally,  it  is  very 
vascular. 

Just  outside  of  this  fold,  the  primitive  uro-genital  sinus 
spreads  to  form  the  Vestibule  of  the  vagina.  This  is  a 
triangular  space,  with  the  apex  formed  by  the  junction  of  the 
labia  minora,  the  sides  by  these  folds  and  the  base  by  the 
vaginal  orifice.  It  contains  the  opening  of  the  urethra.  This 
space  is  lined  by  stratified  sqnanvons  cells.  In  the  tunica 
propria,  are  found  a  great  many  elastic  fibres  and  mucous 
and  sebaceous  glands,  especially  near  the  opening  of  the 
urethra.  The  lower  portion  of  the  tunica  propria  contains 
so  many  large  venous  channels  that  it  is  practically  erectile 

TISSUE. 

Opening  into  the  vestibule  upon  each  side  is  a  gland,  the 


196  THE   FEMALE   GENITAL   SYSTEM. 

analog  of  the  gland  of  Cowper  of  the  male.  This  is  the  gland 
OF  Bartholin,,  which  is  a  compound  racemose  gland,  and 
the  acini  are  lined  by  large,  clear,  mucous  cells.  The  ducts  are 
lined  by  low  columnar  cells. 

Covering  the  vaginal  orifice,  to  a  greater  or  less  extent, 
are  seen  the  Labia  Minora,  or  Nymphae.  These  consist 
of  a  central  mass  of  loose  connective  tissue,  in  which  the 
blood-vessels  are  abundant,  especially  the  veins.  In  the  tis- 
sue between  the  veins,  smooth  muscle  tissue  exists,  and  this 
with  the  vascularity,  forms  to  erectile  tissue.  The  folds 
are  covered,  upon  both  sides,  by  stratified  squamous  cells 
that  rest  upon  a  papillated  tunica  propria.  In  these  papillae, 
capillary  plexuses  are  seen.  Sebaceous  glands  are  numerous, 
but  hairs  and  sweat-glands  are  absent. 

The  Glans  Clitoris  lies  in  the  tissue  formed  by  the  junc- 
tion of  the  labia  minora.  It  is  covered  by  stratified  squam- 
ous cells.  The  central  part  consists  of  erectile  tissue,  and 
many  large  and  small  vascular  papillae  are  present.  Geni- 
tal corpuscles  and  sebaceous  glands  are  found.  The 
Glans  is  covered  by  a  fold  of  skin,  the  prepuce,  in  which 
the  sebaceous  glands  are  quite  numerous. 

The  Labia  Majora  are  merely  folds,  or  pouches  of  skin. 
Their  outer  surfaces  are  covered  by  ordinary  skin.  In  the 
subcutaneous  tissue  ar^  seen  numerous  vessels,  nerves, 
glands,  bundles  of  smooth  muscle  and  an  abundance  of  adi- 
pose tissue.  Along  a  median  line,  they  come  in  contact  with 
each  other,  and  the  skin  surface  is  somewhat  modified.  Here 
elasic  and  muscle  tissues  are  abundant,  but  adipose  tissue  is 
wanting.  The  skin  of  the  labia  majora  is  somewhat  darker 
than  that  in  the  immediate  neighborhood,  owing  to  the  pres- 
ence of  pigment  in  the  epithelial  layers.  Over  the  pubis,  the 
two  labia  meet  and  form  a  prominent  mass,  the  Mons 
Veneris. 


CELLS  LINING  FEMALE  GENITAL  TRACT.  I97 

The  various  portions  of  the  female  genital  tract  are  lined 
by  the  following  cells  : 

Fallopian  Tube Simple  ciliated. 

Uterus. 

Body Simple  ciliated. 

Cervix,  Uterine  end Simple  ciliated. 

Vaginal  end Stratified  squamous. 

Vagina Stratified  squamous. 

Vestibule Stratified  squamous. 

Labia Stratified  squamous. 


CHAPTER  XV. 


THE  PLACENTA  AND  UMBILICAL 
CORD. 

A  description  of  the  formation  of  the  Placenta  and  Cord 
must  be  given,  in  order  to  understand  their  structure  at 
term. 

Should  the  ovum  become  fertilized,  it  is  passed  down  the 
Fallopian  tube  by  the  ciliated  cells,  as  fertilization  usually 
occurs  in  this  portion  of  the  genital  system.  It  is  surrounded 
by  the  zona  pelliicida  and  corona,  or  !:ona  radiata.  The 
mucous  membrane  of  the  uterus  becomes  thickened,  as  for 
menstruation,  and  the  ovum  becomes  lodged,  usually  in  the 
fundus. 

The  mucosa  of  the  uterus  is  divided  into  regions ;  that 
immediately  beneath  the  ovum  is  the  placental  decidua,  or 
DECiDUA  SEROTiNA ;  the  ovum  becomes  covered  by  a  portion 
called  the  ovular,  or  reflex  decidua  ;  the  remainder  is  the 

UTERINE  DECIDUA,   or  DECIDUA   VERA. 

The  ovum  divides  and  redivides,  and  passes  down  the 
Fallopian  tube  towards  the  uterus.  These  cells  form  an  ir- 
regular mass,  the  morula.  The  outer  cells  of  this  mass  ar- 
range themselves  beneath  the  zona  pellucida  as  the  sub- 
zonal  ECTODERM,  or  OUTER  CELL  MASS,  while  the  remainder 
constitute  the  inner  cell  mass.  The  entire  structure  grows 
rapidly,  and,  as  a  result,  a  cavity  is  formed  around  the  inner 
mass,  except  at  one  point,  where  it  is  attached  to  the  sub- 
zonal  layer.  The  cavity  is  filled  with  liquid,  under  pressure. 
This  mass  is  called  the  blastula,  or  one-layered  vesicle. 
The  point  of  attachment  is  called  the  embryonic'  area.  In 
this  condition,  the  ovum  usually  reaches  the  uterus. 

The  outer  mass,  at  the  point  of  union  with  the  inner  mass, 

198 


TRIPOBLAST.  I99 

becomes  greatly  thickened,  its  upper  portion  being  called  the 
TROPHODERM  (Minot),  and  its  under  portion  the  ectoderm. 
The  trophoderm  extends  all  around  the  zona  pellucida,  and 
is  closely  applied  to  it.  The  innermost  cells  of  the  inner 
MASS  then  arrange  themselves  as  a  single  layer  of  cuboidal 
cells  that  extend  into  the  cavity  of  the  blastula  and  form, 
by  meeting,  a  little  vesicle,  the  entodermal  vesicle.  By  this 
formation,  the  gastrula,  or  diptoblast,  in  which  two  dis- 
tinct layers,  ectoderm  and  entoderm,  are  seen,  is  completed. 
From  these  two  layers,  the  mesoderm  is  derived.  This  con- 
stitutes   the   TRIPLOBLAST,    or   THREE-LAYERED   VESICLE.       The 


Fig.    73. — Diagram    of    Supposed    Development   of    Primates    {Minot). 

Tro.   Trophoderm ;   Ec.    ectoderm ;    Mes.    mesoderm ;    Ent.    entoderm ;    Coe. 
coelom. 

mesoderm  lies  between  the  ectoderm  and  entoderm,  and 
where  these  layers  separate,  it  splits  into  two  layers,  one  of 
which  accompanies  the  ectoderm  around  the  diploblast  to 
form  the  somatopleure,  and  the  other  accompanies  the  en- 
toderm to  form  the  splanchnopleure.  The  mass  increases 
in  size,  and  the  trophoderm  in  the  embryonic  area  thickens 
greatly.  At  the  same  time,  the  cells  at  the  junction  of  tropho- 
derm and  ectoderm  disappear,  leaving  a  space,  the  amniotic 
CAVITY.  This  cavity  is  now  bounded  by  trophoderm  above 
and  the  combined  ectoderm,  micsoderm  and  entoderm  be- 
neath, these  latter  constituting  the  embryonic  shield.     At 


200  THE  PLACENTA  AND  UMBILICAL   CORD. 

the  edges  of  the  cavity,  the  mesoderm  continues  with  the 
trophoderm,  forming  the  prochorion. 

At  what  are  to  be  the  cephalad  and  caudad  regions  of 
the  future  embryo,  transverse  depressions  appear  in  the 
somatopleure  (one  at  each  end)  ;  these  are  called  the  head 
and  tail  folds  of  the  amnion,  respectively.  The  lateral  folds 
appear  on  each  side  in  the  same  manner.  All  these  grooves 
deepen,  and  the  somatopleure  extends  ventrally  from  all  di- 
rections (less  from  caudad)  to  form  the  body-wall;  its  re- 


FiG.   74. — Diagram  of   Early   Development  op  Primates.     Later   Stage 
of   73    iMinot). 

a.  Amniotic  cavity;  b.  ectoderm;  c  and  d.  mesoderm;  e.  entoderm. 


turn  folds  pass  dorsally  over  the  embryo  to  unite,  forming 
an  inner  membrane  next  to  the  embryo,  the  true  amnion,  and 
an  outer  above  the  embryo,  the  false  amnion,  or  primitive 
CHORION.  The  prochorion  consists  of  trophoderm  (ecto- 
derm) and  mesoderm ;  the  amnion,  of  mesoderm  and  ecto- 
derm, and  the  body-wall  of  ectoderm  and  mesoderm,  re- 
spectively. At  all  points,  like  layers  are  opposed  to  like 
layers.  In  the  formation  of  the  body-wall  and  amnion,  the 
SPLANCHNOPLEURE  has  been  pushed  before  the  somatopleure 


ALLANTOIS.  201 

to  form  a  tube  within  the  body,  the  gut-tract  and  a  sac  out- 
side, the  YOLK  SAC  and  vitelline  duct. 

In  the  formation  of  the  amnion,  the  embryo  loses  its  con- 
nection with  the  chorion  at  all  points,  except  caudally,  where 
the  mesoderm  and  ectoderm  of  the  two  are  continuous,  form- 
ing the  BELLY-STALK. 

By  this  time,  the  ovum  has  become  lodged  in  the  uterine 
mucosa.  This  process  is  accomplished  by  the  aid  of  the 
trophodermal  cells,  that  have  the  power  of  phagocytosis  (de- 
struction of  tissue)  and  erode  the  superficial  tissues  of  the 
mucosa,  forming  a  cavity  into  which  the  ovum  sinks.  The 
epithelium  of  the  uterus  is  lost  in  this  region  and  also  in  the 
glands  and  the  superficial  vessels  exposed.  The  trophoderm 
becomes  thrown  into  little  processes,  or  villi,  (present  as 
early  as  the  fifth  day,  Peters)  due  to  actual  growth  and  the 
disappearance  of  cells  in  the  trophodermal  layer.  As  a  re- 
sult, there  are  formed  a  series  of  intercommunicating  spaces. 
The  villi  are  composed  of  trophoderm  and  mesoderm.  When 
the  vessels  of  the  mucosa  are  exposed,  they  rupture  into  the 
glandular  spaces,  and  from  these,  the  maternal  blood  gains 
access  to  the  trophodermal  lacunae,  or  spaces.  Thus  does 
the  embryo  receive  nourishment  from  the  mother,  before 
the  umbilical  vessels  are  present.  The  area  of  the  ovum  left 
uncovered  when  the  ovum  becomes  lodged,  is  covered  by 
mucosa  that  is  reflected  from  the  lining  at  the  sides  of  the 
ovum.  This  is,  therefore,  called  decidua  reflexa,  or  ovu- 
lar DECIDUA. 

We  must  rememiber  that  the  belly-stalk  connects  the  em- 
bryo with  the  prochorion.  This  belly-stalk  is  of  importance, 
because  into  it  grows  an  evagination  of  the  caudal  end  of  the 
guttract,  near  its  cloacal  end.  This  evagination  grows  out 
of  the  body  before  the  body-wall  is  formed  in  the  caudal 
region,  and  is  called  the  allantois.     In  some  animals,  the 


202  THE   PLACENTA   AND   UMBILICAL   CORD. 

OVIPAROUS,  the  allantois  loses  connection  zmth  the  belly-stalk, 
and  is  free.  It  remains  as  a  dilated  sac,  and  serves  as  a 
receptacle  for  urine.  In  the  viviparous  animals,  it  remains 
connected  with  the  belly-stalk,  and  connects  permanently  the 
embryo  with  the  uterus,  becoming  the  organ  of  nutrition  and 
respiration.  Its  outer  ends  spread  along  the  inner  surface, 
carrying  splanchnic  mesoderm  to  the  villi  of  the  avascular 


Fig.    75. — Diagram   of   Early   Development   of   I'rimates.     Later   than 

Fis.    74    (Minot). 

a.  Amnion  ;  6.  chorion  ;  c.  embryo  ;  d.  yolk-sac ;  e.  body-stalk  ;  f.  allantois  ; 

g.  entodermal  cavity  of  embryo  ;  h.  entoderm  ;  i.  chorionic  villi. 

prochorion,  and  with  the  latter  structure  it  forms  the  true 
CHORION.  In  this  mesoderm,  four  main  vessels  develop,  tzvo 
arteries  and  tzvo  veins.  The  two  veins  enter  the  body  and 
proceed  towards  the  heart,  while  the  other  two  pass  into  the 
body,  and  connect  with  the  aorta.  The  distal  ends  of  all  the 
vessels  pass  into  the  chorion,  and  divide  to  supply  all  the  villi. 
These  villi  are  still  covered  by  the  trophodenn,  consisting 


CHORION.  203 

usually  of  two  layers.  Of  these,  the  outer  becomes  converted 
into  a  thin  layer  of  protoplasm,  in  which  the  original  nuclei 
remain.     This   protoplasm  constitutes   the  syncytium. 

The  villi  do  not  long  remain  simple,  but  branch  and  re- 
branch ;  the  vessels  follow  these  branches,  and  penetrate  to 
the  very  ends.  Some  of  the  villi  enter  the  uterine  glands, 
in  which  the  epithelium  becomes  denuded  by  about  the  sixth 
week,  and  the  surface  cells  by  the  fourth  week,  and  are  the 
floating  villi;  others  become  attached,  and  form  the  Hxed 
villi.  When  the  epithelium  of  the  uterus  is  lost,  the  en- 
gorged superficial  capillaries  of  the  placental  decidua  become 
connected  with  the  glands,  and  the  blood  enters  these,  and 
then  the  trophodermal  spaces.  These  channels  are  the  later 
interznllous  spaces.  From  these  cavities,  the  blood  is  re- 
turned to  the  venous  channels  of  the  mucosa,  but  no  direct 
connection  is  established  betzveen  vhe  fetns  and  the  mother. 

These  villi  are  very  abundant,  and  may  be  scattered  all 
over  the  ovum,  or  be  limited  to  the  equator  of  the  mass. 
Up  to  this  time,  all  are  equal  in  size.  Soon  a  difference  is 
noted  in  size,  those  at  the  place  of  attachment  of  the  ovum 
increase  in  number  and  size,  forming  the  chorion  frondo- 
sum,  while  the  remainder  disappear  and  constitute  the 
chorion  laeve. 

At  about  the  fifth  month,  a  villus  has  the  following  ap- 
pearance. Of  the  trophodermal  cells,  the  outer  do  not  re- 
main large,  distinct  elements,  but  become  flattened,  and  rep- 
resent a  mere  layer  of  nucleated  protoplasm  that  covers  the 
villi ;  this  is  the  syncytium,  and  it  is  the  covering  of  the  em- 
bryonic connective  tissue  that  constitutes  the  core  of  the  villi 
and  supports  the  vessels.  In  the  inner  layer,  the  cells  re- 
main distinctly  outlined,  and  persist,  for  a  short  time,  as  the 
cell-layer  of  Langhans.  From  the  fifth  month  on,  they 
disappear   so   that   ultimately  only   the   syncytium   remains. 


204 


THE   PLACENTA   AND   UMBILICAL   CORD. 


Here  and  there  in  the  villi  are  seen  groups  of  cells  that  rep- 
resent collections  of  syncytial  cells,  the  cell  knots.  These, 
like  the  other  syncytium,  contain  nuclei  that  are  small,  but 
stain   deeply.     The  protoplasm   responds   well   to  the   acid 


Fig.  76. — Semi-Diagrammatic  Outline  of  an  Antero-Posterior  Section 
OF  A  Human  Uterus  Containing  an  Embryo  of  About  Five  Weeks. 

a.  Anterior ;  p.  posterior  surface  ;  g.  outer  limit  of  decidua ;  s,  s.  limits 
of  the  decidua  serotina ;  ch.  chorion,  within  which  is  the  embryo  en- 
closed by  the  amnion,  and  attached  to  the  chorion  by  the  umbilical 
cord  ;  from  the  cord  hangs  the  pedunculated  yolk-sac ;  r,  r.  decidua 
reflexa    (Minot). 


Stains.     The  Langhans  cells,  however,  contain  large  nuclei, 
but  neither  these  nor  the  protoplasm  respond  well  to  stains. 

After  the  third  month,  the  number  of  villi  that  becomes 
attached  to  the  mucosa  rapidly  increases,  so  that  after  that 


PLACENTA.  205 

time,  the  fetal  and  maternal  portions  become  more  and  more 
fixed  to  each  other. 

This  is  the  beginning  of  the  formation  of  the  placenta, 
such  as  it  is  seen  at  birth.  The  villi  branch  repeatedly,  and 
the  whole  structure  grows  rapidly,  causing  the  child  to  do 
the  same.  Any  disturbance  that  will  retard  the  growth  of 
the  placenta  will  also  retard  the  growth  of  the  fetus  in  great  • 
er  proportion.  The  difference  between  the  placenta  at  the 
fourth  or  fifth  month,  and  at  birth,  is  merely  in  size.  This 
is  due  to  the  increase  in  number  and  branches  of  the  villi 
The  villi  are  separated  into  groups  by  connective  tissue  septa 
that  are  derived  from  the  uterine  tunica  propria.  These 
are  the  placental  sepfae. 

At  birth,  the  Placenta  is  a  flesh-like,  saucer-shaped  mass, 
the  attached  surface  of  which  is  divided  into  lobes,  or  cotyle- 
dons. The  fetal  surface  is  covered  by  the  amnion,  a  con- 
tinuation of  the  sac  in  which  the  fetus  lies,  and  shows  the 
vessels  as  they  enter  and  leave  the  organ ;  the  opposite  sur- 
face is  divided  inco  lobes,  or  cotyledons,  covered  by  the  de- 
cidua  serotina.  The  weight  of  the  placenta  is  about  one-sixth 
that  of  the  child.  It  consists  of  two  portions,  the  fetal  and 
maternal. 

This  organ  consists  of  a  fleshy  miass  lying  between  two 
membranes.  Upon  the  fetal  surface,  we  find  the  amnion 
and  CHORION.  The  amnion  consists  of  a  single  layer  of 
cuboidal  epithelial  cells  that  rest  upon  the  mesodermal  tis- 
sue. These  epithelial  cells  possess  prominent,  deeply-stain- 
ing nuclei,  but  the  protoplasm  does  not  react  well  to  the 
stain.  The  mesodermal  tissue  is  somewhat  fibrillar,  and  few 
cells  are  present.     It  is  avascular. 

The  chorion  is  comiposed  of  mesodermal  tissue,  in  which 
the  fibrils  are  more  or  less  distinct.  From  the  side  opposite 
to  the  amnion  are  seen  projections.     These  may  vary  from 


2o6 


THE   PLACENTA   AND   UMBILICAL   CORD. 


small  simple  villi,  to  those  resembling  a  tree  possessing  an 
enormous  number  of  twigs.  Along  this  surface  of  the  chor- 
ion, may  be  seen  masses  of  a  fibrillar  substance  that  are 


Fig.  77. — Human  Placenta  at  Term. 
A.  Vertical  section  at  margin  ;  D.  decidua  :  Cho.  chorion ;  Fih.  fibrin  :  Vi. 
placental  villi ;  Si.  marginal  sinus ;  vi.  aborted  extra-placental  villi ; 
J),  decidual  tissue.  B.  Portion  of  decidual  tissue  at  b  highly  magnified  ; 
V.  blood-vesseis ;  d.  deciuual  cells  with  one  nucleus ;  d'.  multinucle- 
ated  decidual   cells    (Minot). 


called  canalized  Hhrin.  The  bulk  of  the  placenta  consists  of 
villi.  These  form  a  reddish,  spongy  mass,  divided  into 
masses  called  cotyledons.     The  main  stems  contain  two  or 


MEMBRANES.  '  20/ 

more  vessels  surrounded  by  mesodermal  tissue.  Peripheral- 
ly, each  villus  is  covered  by  a  thin  layer  of  nucleated  proto- 
plasm, the  syncythun.  The  small  twigs  consist  of  a  core 
of  mucous  connective  tissue  supporting  several  small  capil- 
laries. The  syncytium  surrounds  each  twig.  In  places  are 
seen  collections  of  nuclei  representing  the  cell-knots.  The 
cavities  between  the  villi  are  the  intervillous  spaces  contain- 
ing the  maternal  blood  and,  at  times,  canalized  fibrin. 

From  this,  it  is  readily  seen  that  the  fetal  and  maternal 
blood  currents  do  not  intermingle.  They  are  separated 
from  each  other,  the  endothelium  of  the  fetal  capillaries  on 
the  one  hand,  and  the  syncytium  of  the  villi  on  the  other. 

The    maternal    side    of   the    placenta   is    covered   by    the 

DECIDUA  SEROTINA,   Or  the   STRATUM   COMPACTUM   of  the   mu- 

cosa.  It  is  less  than  a  millimeter  thick,  and  possesses  a 
number  of  short,  oblique  channels.  These  are  the  remains 
of  the  uterine  glands ;  they  now  represent  blood  sinuses, 
which  contain  maternal  blood. 

The  serotina  extends  into  the  fetal  portion  as  the  placental 
septae,  and  divides  it  into  the  cotyledons.  At  the  edge  of 
the  placenta,  it  becomes  attached  to  the  chorion,  and  con- 
tinues as  the  DECIDUA  vera.  At  this  junction,  there  is  a  con- 
siderable space  that  extends  all  around  the  edge  of  the  pla- 
centa. This  is  the  marginal  'sinus,  and  is  prominent  be- 
cause few,  or  no,  villi  have  developed  here. 

The  MEMBRANES  consist  of  the  amnion  and  the  uterine 
lining,  or  the  stratum  compactum.  The  latter  is  thin,  and 
contains  neither  glands  nor  epithelium.  When  the  fetus  in- 
creases in  size  and  causes  a  dilatation  of  the  uterus,  the 
amniotic  sac  is  forced  against  the  uterine  lining,  and  causes 
an  atrophy  of  the  glands  and  cells  of  the  stratum  compact- 
um. As  a  result,  a  mere  fibrinous  membrane,  that  has  a  loose 
connection  with  the  amnion,  is  produced,  due  entirely  to 
pressure. 


208    '  THE   PLACENTA   AND   UMBILICAL   CORD. 

The  Umbilical  Cord  is  the  connecting  link  between  the 
fetus  and  the  placenta,  and  represents  the  early  allantoic 
stalk.  It  is  surrounded  by  one  or  more  layers  of  cuboidal  epi- 
theHal  cells  continuous  on  the  one  hand  with  epithelium  of 
the  amnion,  and  on  the  other,  with  the  ectodermal  cells  of  the 
body,  supported  by  a  little  subepithelial  fibrous  tissue.  Within 
this  covering  is  the  pecuHar  tissue  called  Wharton's  jelly. 


Fig.  78. — Cross-section  of  Human  Umbilical  Cord  (Miriot). 
A,  A'.  Umbilical  arteries ;  V.  umbilical  vein  ;   Y.  remains  of  allantois. 

This  is  embryonic  connective  tissue  in  which  the  cells 
are  chiefly  spindle-shaped;  some  round  and  stellate  cells, 
however,  are  seen.  The  intercellular  substance  is  semi-solid, 
and  takes  a  peculiar  homogeneous  stain.  During  the  early 
months  of  pregnancy,  the  intercellular  substance  contains  a 
great  deal  of  water,  and  the  cellular  elements  are  few.  At 
the  end  of  pregnancy,  the  intercellular  substance  is  more 
or  less  fibrillar,  though  the  semi-solid  portion  predominates. 
At  this  time,  the  cells  are  mostly  of  the  stellate  type,  but  not 
numerous.  At  the  body  end,  occasionally,  traces  of  allan- 
toic cavity  and  yolk  sac  are  found. 

The  VESSELS  contained  are  the  single  umbilical  vein  and 
two  UMBILICAL  ARTERIES.  Thesc  are  thick-walled  and  well 
developed,  and  the  muscle  fibres  run  both  circularly  and 


FETAL    CIRCULATION.  20g 

longitudinally.  The  wall  of  the  arteries  is  thicker  than  that 
of  the  vein.  The  insertion  of  the  cord  into  the  placenta  is 
usually  eccentric,  and,  at  this  point,  the  vessels  branch  rapid- 
ly, and  spread  out  in  all  directions. 

The  circulation  of  the  placenta  is  a  closed  one.  The  blood 
is  carried  from  the  iliac  arteries  to  the  umbilicus  through  the 
hypogastric  arteries,  which  continue  in  the  cord  as  the  um- 
bilical arteries.  These  branch  to  follow  the  villi,  and,  ulti- 
mately, terminate  in  tufts  of  capillaries  in  the  terminal  vil- 
lous twigs.  The  blood  at  this  point  receives  the  oxygen  and 
nutritive  matter  from  the  maternal  blood  that  circulates  in 
the  intervillous  spaces  in  which  the  villi  lie.  There  is  no 
direct  communication  between  the  fetal  and  mxiternal  blood, 
for  they  are  separated  from  each  other  by  the  endothelium 
of  the  capillaries,  and  the  syncytium  covering  the  villi.  As 
the  oxygen  and  nutritious  substances  pass  into  the  fetal 
blood,  the  effete  matter  and  gases  pass  out  into  the  maternal 
blood.  The  principle  is  the  same  as  in  the  lung,  where  the 
blood  is  oxygenated.  Red  cells  never  pass  from  one  systeni 
to  another,  but  leukocytes  that  have  the  power  of  ameboid 
motion  may.  The  blood  is  collected  by  the  radicals  of  the 
mnbilical  vein,  and  carried  into  the  body  to  the  under  surface 
of  the  liver,  where  the  greater  portion  enters  the  portal 
vein,  through  the  continuation  of  the  umbilical  vein,  and  the 
remainder  is  carried  to  the  inferior  cava  by  the  ductus  ven- 
osus.  The  blood  passes  to  the  right  auricle,  then  through  the 
foramen  ovale  to  the  left  auricle,  from  which  it  passes, 
through  the  auriculo-ventricular  orifice,  into  the  left  ven- 
tricle. The  blood  then  passes  into  the  aorta  chiefly  to  the 
upper  extremities  and  head,  is  collected  by  the  radicals 
of  the  superior  vena  cava,  and  emptied  into  the  right  auricle. 
From  this  chamber,  it  passes  through  the  auriculo-ventricu- 
lar orifice  into  the  right  ventricle,  from  which  it  passes  into 
the  pulmonary  artery  towards  the  lungs.     As  these  organs 


2IO  THE   PLACENTA   AND   UMBILICAL   CORD. 

do  not  functionate  at  this  time,  most  of  the  blood  is  sent  to 
the  aorta  through  the  ductus  arteriosus.  The  blood  then 
passes  towards  the  lower  extremities,  and,  as  it  reaches  the 
internal  iliac  arteries,  most  of  it  is  sent  to  the  placenta 
through  the  arterial  trunks,  which,  inside  of  the  body,  are 
called  the  hypogastric  arteries,  and  in  the  cord  the  umbilical 
arteries. 


CHAPTER  XVI. 


THE  SKIN  AND  ITS  APPENDAGES. 

The  Skin  covers  the  external  surface  of  the  body,  and  is 
its  most  extensive  organ.  It  consists  of  two  portions,  the 
Epidermis,  or  Cuticle,  and  the  Cutis  Vera,  or  Corium. 

The  Epidermis  is  the  epithelial  portion  of  which  appen- 
dages are  modifications.  It  consists  of  stratified  squamous 
cells,  which,  over  the  general  body  surface,  are  divisible  into 
tzvo  layers,  stratum  Malpighii  and  stratum  corneum. 

The  STRATUM  Malpighii,  or  rete  mucosum,  is  composed 
of  a  number  of  layers  of  cells.  The  basal  part  consists  of 
columnar  elements,  and  is  called  the  genetic  layer.  The 
cells  stain  deeply,  and  under  certain  conditions  show  pigment 
granules.  The  layer  is  uneven  in  its  course,  as  it  conforms 
to  the  waves  of  the  corium.  The  upper  cells  of  the  stratum 
Malpighii  are  large,  polyhedral  elements  that  do  not  touch 
one  another,  but  are  separated  by  intercellular  spaces.  Each 
cell  is  provided  with  a  number  of  delicate  spines,  or  prickles, 
that  meet  those  of  other  cells,  and  thus  prevent  the  cell- 
bodies  from  coming  in  contact  with  one  another.  These  are 
the  prickle  cells.  As  the  upper  part  of  this  stratum  is  ap- 
proached, the  cells  becom.e  flattened,  and  have  an  even 
course. 

The  STRATUM  CORNEUM  ordinarily  forms  a  thin  layer.  Its 
cells  are  very  thin  and  scale-like,  and  usually  possess  no 
nuclei.  They  are  derived  from  the  cells  beneath,  but  differ 
from  them  in  consisting  of  keratin  that  gives  them  their 
hard  and  horny  characteristic.  These  cells  are  constantly 
cast  off,  and  the  cells  below  increase  to  replace  them.  Be- 
tween these  two  layers  an  irregular  stratum  granulosum 
is  often  seen. 

211 


212  THE   SKIN    AND    ITS    APPENDAGES. 

In  certain  parts  of  the  body,  sole  and  palm,  the  stratum 
GRANULOSUM  and  another,  the  stratum  lucidum,  are  well 
developed. 

The  STRATUM  GRANULOSUM  lies  jiist  above  the  stratum 
Malpighii,  and  is  composed  of  two  or  three  layers  of  flattened, 
spindle-shaped  cells  that  contain  a  deeply-staining  nucleus 
and  coarsely  granular  protoplasm.  The  granules  are  kcra- 
tohyalin,  that,  later,  form  the  horny  matter  of  the  stratum 
corneum.  These  granules  are  quite  large  and  prominent,  and 
respond  well  to  hematoxylin.  They  seem  to  be  modified 
protoplasm,  but  some  hold  that  they  represent  products  of 
the  degenerating  nucleus. 

The  STRATUM  LUCiDUM  lies  just  above  the  stratum  granu- 
losum,  and  separates  this  from  the  stratum  corneum.  It 
forms  a  narrow,  glistening  band  of  cells,  two  or  three  layers 
broad,  in  which  the  keratohyalin  granules  have  fused  to  form 
a  homogeneous  substance,  called  the  eleidin.  This  substance 
reacts  well  to  eosin.  The  nuclei  are  not  prominent,  nor  are 
the  cell-bodies  distinct. 

The  Derma,  True  Skin,  or  Cutis  Vera,  is  composed  of 
connective  tissue  arranged  in  two  more  or  less  distinctly- 
separated  layers.  These  are  the  stratum  papillare,  or 
upper,  and  the  stratum  reticulars,  or  lower. 

The  stratum  papillare  consists  of  delicate  bundles  of 
small  white  fibrils  forming  a  "close  network  with  elastic 
fibres. 

The  upper  portion  of  this  stratum  is  thrown  into  small 
waves  called  the  papillae,  to  which  the  stratum  Malpighii 
conforms.  Over  the  general  skin  surface,  these  papillae  do 
not  extend  through  the  stratum  Malpighii,  but  in  the  palmar 
and  plantar  regions  they  are  visible  externally,  and  cause  the 
peculiar  markings  seen  in  these  areas.  These  papillae  are 
important,  as  they  contain  either  capillary  plexuses,  or  spe- 


DERMA. 


213 


cial  sensory  nerve  endings.  The  lower  portion  of  the  papil- 
lare  consists  of  a  looser  network,  in  which  the  vessels  form 
plexuses  parallel  with  the  surface.     It  gradually  passes  into 

the  STRATUM    RETICULARE. 


Fig.  79. — Cross-section  of  Skin  of  Sole  of  Foot. 
Stratum  corneum  ;  h.  stratum  lucidum  ;  c.  stratum  granulosum  ;  d.  stra- 
tum Malpighii ;  e.  derma ;  f.  panniculus  adiposis ;  g.  duct  of  sweat 
gland  :  h.  prickle  cells  :  i.  genetic  layer ;  k.  cross-section  of  a  smooth 
muscle  fibre  ;  I.  duct  of  sweat  gland  ;  m.  Pacinian  body  ;  n.  secretory 
portion  of  sweat  gland  ;  0.  muscle  of  tubule  ;  p.  blood-vessel ;  q.  adi- 
pose tissue. 


The  STRATUM  RETICULARE  is  not  distinctly  separable  from 
the  preceding.  It  is  composed  of  larger  bundles  of  coarser 
fibrils  of  white  fibrous  tissue,  and  contains  some  yellow  elas- 
tic tissue,  as  will  be  seen  below.    Here  are  found  the  larger 


214  THE   SKIN    AND    ITS    APPENDAGES. 

blood-vessels  and  the  appendages  and  special  sensory  nerve 
endings.  In  the  corium  of  the  scrotum,  penis  and  nipple, 
smooth  muscle  fibres  are  found.  When  these  bundles  con- 
tract, "goose-flesh"  is  produced. 

The  elastica  is  often  separated  into  layers,  of  which  there 
are  four,  the  subepithelial,  papillary,  reticular  and  subcutan- 
eous elastic  layers. 

Beneath  the  stratum  reticulare  is  usually  a  layer  of  adi- 
pose tissue  that  separates  the  skin  from  the  fascia.  This  is 
the  PANNicuLus  ADiPOSUS,  and  it  varies  in  thickness  in  the 
different  regions. 

The  color  of  the  skin  is  due  to  the  presence  of  pigment 
granules  in  the  lower  layers  of  the  stratum  Malpighii.  Such 
granules  have  been  found  even  in  the  corium.  In  the  white 
races,  this  pigmentation  is  limited  to  the  nipple  and  genital 
region.  Whether  the  pigment  is  due  to  the  vital  activity 
of  the  cells,  or  whether  it  is  brought  here  and  deposited,  is 
not  definitely  settled.  The  former  seems  to  be  the  origin 
of  that  of  the  retinal  cells. 

The  skin  is  the  protective  organ,  and  varies  in  thickness  in 
the  different  regions.  It  is  thinner  on  the  less  exposed  sur- 
faces, as  the  inner  surfaces  of  the  thighs  and  arms,  and 
thicker  on  the  exposed  regions,  as  back,  sole  and  palm. 

The  blood-vessels  of  the  skin  vary  in  size  and  number, 
according  to  the  location ;  in  the  gluteal,  plantar  and  palmar 
regions,  they  are  greater,  whil^in  the  most  movable  parts 
they  are  most  branched.  The  larger  trunks  lie  in  the  reticu- 
lare, parallel  to  the  surface,  and  form  a  capillary  plexus  in 
the  papillare.  From  this  plexus,  capillary  tufts  enter  the 
various  papillae.  The  latter  vessels  continue  as  venous  cap- 
illaries, that  form  a  plexus  just  beneath  the  papillae.  This 
empties  into  another  in  the  lower  portion  of  the  derma  that 
communicates  with  a  subdermal  plexus ;  the  latter  lies  be- 


APPENDAGES.  215 

twcen  the  derma  and  the  panniculus  adiposus,  and  its  ves- 
sels possess  valves. 

The  long  nerve  trunks  are  found  in  the  reticulare,  and 
from  these  branches  form  a  suhpapillary  plexus.  Medul- 
lated  fibres  extend  towards  the  surface,  and  form  the  special 
endings. 

The  nerve  endings  are  very  numerous  in  the  skin.  These 
comprise  the  free  endings,  or  those  in  which  the  naked  axis 
cylinder  pierce  the  epithelial  layer,  branch  and  send  these 
divisions  between  epithelial  cells.  The  higher  forms  of  end- 
ings comprise  tactile  corpuscles  of  Meissner,  most  numerous 
in  the  palmar  and  plantar  skin  of  the  fingers  and  toes ;  end 
bulbs  of  the  conjunctiva  and  gentalia;  Pacinian  bodies  espe- 
cially in  the  palms  and  soles ;  and  the  organs  of  RufUni,  re- 
sembling the  neuro-muscular  endings.  For  a  detailed  de- 
scription, see  Nerve  Endings  (p.  82).  In  addition,  there 
is  the  usual  nerve  supply  to  the  blood-vessels. 

The  lymplmtics  of  the  skin  consist  of  superficial,  or  papil- 
lary plexus,  which  receives  the  lymph  from  the  spaces  in 
the  papillae,  and  a  deeper,  or  subcutaneous  plexus  that  con- 
sists of  larger  trunks,  that  anastomose  with  the  above,  and 
communicate  with  the  special  plexuses  of  the  appendages. 

THE  APPENDAGES. 

The  Appendages  of  the  skin  are  the  Hairs,  Nails,  Se- 
baceous, Sweat  and  Mammary  Glands.  These  are  all  de- 
rived from  the  epidermis. 

THE  HAIRS. 

The  Hairs  are  protective  organs  limited  to  certain  por- 
tions of  the  body.  Each  consists  of  a  root,  that  portion  with- 
in the  skin,  and  a  shaft,  that  part  seen  above  the  surface. 

The  ROOT  is  somewhat  flask-shaped,  the  lower  end  being 
enlarged  to  form  the  iiair-bulb.    This,  on  its  under  surface, 


2l6 


THE   SKIN    AND    ITS    APPENDAGES. 


is  indented  and  invaginated  by  a  little  mass  of  connective 
tissue,  the  hair  papilla,  that  contains  a  small  tuft  of  capil- 
laries, upon  which  the  nourishment  of  the  hair  solely  de- 
pends. The  root  is  surrounded  by  a  condensation  of  the 
derma,  in  which  the  connective  tissue  bundles  are  arranged 
into  two  layers. 


Fig.  80. — From  Section  of  Scalp   {Stohr's  Histology). 

1.  Hair-shaft ;  2.  hair-root ;  3.  sebaceous  gland  ;  4.  arrector  pili  muscle ; 
5.  root-sheaths ;  6.  follicular  sheath ;  7.  hair-bulb ;  8.  papilla ; 
9.   fat  cells. 


In  the  outer,  the  fibres  have  a  longitudinal  course,  while 
in  the  inner,  they  run  circularly.  Within  this  circular  layer 
is  a  prominent  homogeneous  band,  the  glassy  membrane. 
This  represents  a  greatly  hypertrophied  Z^a^^m^n^  mem- 
brane. These  layers  constitute  the  follicular  sheath. 
Internal  to  it  are  found  the  epithelial  cells,  which  are  contin- 


HAIRS.  217 

nous  with  the  epidermis.  These  are  arranged  into  layers  that 
are  the  root  sheaths,  of  which  there  are  two,  outer  and 

INNER. 

The  OUTER  root  sheath  is  the  direct  continuation  of  the 
stratum  Malpighii.  These  cells  are  the  same  as  elsewhere, 
and  continue  to  the  bottom  of  the  root,  where  they  blend 
with  those  of  the  inner  root  sheath.  Throughout  the  greater 
part  of  the  follicle,  this  layer  consists  of  several  rows  of 
cells.  Toward  the  bulb,  it  gradually  becomes  reduced  to  a 
single  layer. 

The  inner  root  sheath  begins  at  the  lower  edge  of  the 
orifice  of  the  sebaceous  gland  that  opens  into  the  hair  fol- 
licle. Above  the  duct,  it  is  replaced  by  the  stratum  corneum. 
This  sheath  consists  of  two  portions,  the  outer  of  which  is 
called  the  layer  of  Henle.  This  lies  next  to  the  outer 
root  sheath,  and  is  composed  of  a  single  layer  of  flattened 
cells.  Within  this  lawyer  is  the  sheath,  or  layer  of  Huxley, 
which  consists  of  two  or  three  layers  of  large  irregular  cells. 
In  the  bulb,  all  of  these  layers,  including  the  outer  root 
sheath,  are  inseparable,  and  gradually  pass  over  into  the 
hair  itself. 

The  Hair  occupies  the  central  portion  of  the  follicle,  and 
is  composed  of  three  parts,  cuticle,  cortex  and  medulla. 

The  cuticle  is  composed  of  ai  single  layer  of  irregular, 
nonnucleated  scales.  These  are  very  thin,  and  overlap.  With- 
in the  follicle,  they  lie  closely  applied  to  the  layer  of  Huxley. 
The  cortex  consists  of  a  great  many  layers  of  long,  spindle- 
shaped  elements.  The  nuclei  are  rod-shaped.  The  me- 
dulla, when  present,  is  composed  of  several  rows  of  cu- 
boidal  cells  that  do  not  extend  the  length  of  the  hair.  They 
contain  granules  of  keratohyalin,  and  frequently  have  a 
dark  appearance;  this  is  due  to  the  presence  of  small  air- 
bubbles. 


2l8  THE   SKIN    AND    ITS    APPENDAGES. 

The  heaviest  hairs  are  found  on  the  scalp  and  pubis,  in 
the  axilla,  and  upon  the  face  of  males.  Delicate  hairs  occur 
taJl  over  the  body  surface,  and  these  are  like  the  lanugo 
HAIRS  of  the  fetus. 

The  color  of  the  hair  is  due  to  pigment  granules  in  the 
cortex.  These  cells  may  even  contain  pigment  in  solution. 
Diffuse  pigment  is  abundant  in  dark  and  red  hairs,  but  ab- 
sent in  white. 

Opening  into  the  hair  follicles  are  the  sebaceous  glands. 
This  is  usually  upon  the  side  toward  which  the  hair  leans, 
and  here  is  also  seen  the  muscle  of  the  hair  follicle,  the 
arrector  pili  muscle.  This  is  smooth  muscle,  and  is  at- 
tached  above  to  the  derma,  just  beneath  the  stratum  Mal- 
pighii,  and  below  to  the  hair  bulb.  When  it  contracts,  it 
causes  the  hair  to  ''stand  on  end." 

THE  NAILS. 

The  Nails  are  peculiar  appendages  that  serve  for  the 
protection  of  the  ends  of  the  fingers  and  toes,  and  consist  of 
the  ROOT  and  the  nail-body. 

The  ROOT  is  the  proximal  end  at  which  the  organ  grows. 
Here  the  epithelial  cells  are  transformed  into  the  hard  sub- 
stance that  gives  the  nail  its  character.  Along  the  sides, 
the  nail  is  protected  by  an  overhanging  ledge  of  skin,  which 
constitutes,  at  the  root,  the  nail-fold^  and  at  the  sides,  the 
NAIL-3YALL.  The  angle  formeS  by  the  nail  and  wall  is  the 
nail-groove.  The  stratum  corneum  continues  into  the  angle 
over  the  edge  of  the  nail  as  the  eponychium. 

The  NAIL-BODY  consists  of  the  nail  proper  and  the  nail- 
bed  upon  which  the  nail  rests. 

The  nail  represents  a  greatly-hypertrophied  stratum  lu- 
cidum.  The  cells  are  flattened  elements,  in  which  the  nuclei 
are  indistinct,  and  the  protoplasm  clear.  At  the  proximal 
end  is  the  root,  and  at  this  place  alone  the  nail  grows.    It  is 


GLANDS. 


219 


marked  by  a  white  area,  the  lunula.  Here  the  epithelial 
layer  is  so  thick  that  the  underlying  capillaries  are  invisible. 
The  cells  also  are  said  to  contain  keratohyalin  granules.  At 
the  distal  end,  the  nail  projects  as  the  free  edge. 

The  NAIL-BED  consists  of  the  stratum  Malpighii  and  the 
corium.  The  stratum  Malpighii  resembles  that  of  the  skin 
surface,  and  rests  upon  the  papillated  corium.  That  portion 
beneath  the  lunula  is  termed  the  matrix.  The  corium  is 
composed  of  bundles  of  white  fibrous  and  yellow  elastic  tis- 
sues that  have  a  general  longitudinal  direction.     Between 


Fig.    81. — Cross-section    of    Nail. 
1.   Nail;   2.   corium;  3.   epithelium;   4.   nail-wall;   5.  nail  groove;   6.   bone 
of  phalanx  ;  7.  eponychium. 

the  bundles  are  vertical  fibres  that  pass  from  the  periosteum 
towards  the  nail.  The  papillae  of  the  bed  are  not  like  those 
of  the  skin,  but  consist  of  long  ridges  that  extend  from  the 
root  to  the  end  of  the  nail.  They  are  small  beneath  the 
root,  but  increase  in  height  as  the  free  edge  is  approached, 
and  end  abruptly  at  that  point. 

THE  GLANDS. 

The  Glands  comprise  the  Sweat,  Sebaceous  and  Mam- 
mary Glands. 

The  Sweat-Glands  are  of  the  coiled  tubular  variety.  Each 
consists  of  a  secretory  portion,  that  lies  in  the  stratum  reticu- 


220  THE   SKIN    AND    ITS    APPENDAGES. 

lare,  and  an  excretory  duct,  that  passes  up  through  the 
derma  and  cuticle  to  open  upon  the  surface. 

The  SECRETORY  PORTION  coiisists  of  a  single  layer  of  cu- 
hoidal  cells  lining  the  tubule.  These  are  separated  from  the 
basement  membrane  by  a  layer  of  smooth  muscle  fibres. 
The  protoplasm  is  granular,  and  ma-y  contain  pigment  gran- 
ules and  fat  globules.  The  nucleus  is  usually  quite  distinct. 
The  secretory  tubule  is  coiled  upon  itself,  and  the  various 
convolutions  are  separated  from  one  another  by  interstitial 
tissue  that  corresponds  to  the  tunica  propria. 

The  DUCT  that  leads  from  the  secretory  part  to  the  sur- 
face has,  usually,  one-half  the  diameter  of  the  secretory 
tubule,  and  is  lined  by  iwo  layers  of  cells  that  rest  upon  a 
basement  membrane  and  tunica  propria.  In  the  epidermis, 
its  course  is  spiral,  and  no  separate  wall  is  present,  the  epi- 
thelial cells  of  the  epidermis  acting  in  this  capacity.  The 
diameter  of  this  portion  is  greater  than  that  of  the  corium. 
Its  opening  upon  the  surface  is  large  and  trumpet-shaped, 
and  is  called  the  sweat-pore. 

These  glands  are  generally  distributed,  except  on  the  mar- 
gins of  the  lips,  glans  penis  and  inner  surface  of  the  pre- 
puce. T hey' a^i"e  rhbst  numerous  in  the  palm,  and  largest  in 
the  axilla.  The  average  diameter  is  i  mm.,  but  in  the  latter 
region,  they  may  attain  a  size  of  3  or  4  mm.  In  this  region, 
the  secretory  tubule  may  be  branched. 

The  normal  secretion  is  an  oil  that  keeps  the  skin  soft  and 
pliable.  When  the  innervation  becomes  disturbed,  the  se- 
cretion becomes  thin  and  watery,  and  is  then  termed  szveat. 
The  GLANDS  OF  MoLL,  of  the  eyelid,  and  the  ceruminous 
GLANDS  of  the  external  ear,  are  coiled  tubular  "glands  that 
secrete  oil  alone. 

The  Sebaceous  Glands  are  lacemose  structures.  They 
are  usually  found  in  connection  with  the  hair  follicles ;  the 


MAMMARY    GLAND.  221 

largest  hairs  possess  small  glands,  while  the  smallest  hairs 
are  appendages  of  the  attached  sebaceous  glands.  Each 
is  surrounded  by  a  capsule  of  white  fibrous  tissue  that  forms 
the  supportive  structure. 

The  ALVEOLI  are  lined  by  cells  that  are  a  continuation  of 
the  cells  of  the  stratum  Malpighii,  and  which  rest  upon  a 
basement  membrane  and  tunica  propria.  These  cells  are 
very  large,  and  completely  fill  the  ailveolus.  Those  in  the 
center,  where  the  lumen  should  be,  are  further  advanced  in 
changes  than  the  basal  cells.  The  entire  protoplasm^  becomes 
converted  into  oil,  which  constitutes  the  secretion,  and  is 
called  SEBUM.  The  death  of  the  cell  is  necessary  to  the 
formation  of  this  secretion.  The  transformed  cell  is  imme- 
diately replaced  by  another.  The  excretory  duct  is  lined 
by  several  layers  of  cells  that  do  not  ta-ke  part  in  the  secre- 
tory activity,  and  are  derived  from  the  outer  root  sheath  of 
the  hair  follicle. 

Sebaceous  glands  are  found  in  regions  devoid  of  hairs, 
as  in  the  margins  of  the  lips,  glans  penis,  prepuce,  glans 
clitoris  and  labia^  minora. 

THE  MAMMARY   GLAND. 

The  Mammary  Gland  is  an  alveolo-tubular  organ.  Ac- 
cording to  some  writers,  it  is  a  modiUed  sweat-gland,  while 
others  hold  it  to  be  a  modified  sebaceous  structure.  It  is 
a  compound  organ,  if  such  a  term  may  be  used,  as  it  is 
composed  of  from  fifteen  to  twenty  individual  compound 
glands.  Eaich  of  these  possesses  its  own  excretory  duct, 
that  has  its  own  opening  in  the  nipple.  The  entire  organ 
is  covered  by  skin. 

Each  gland  consists  of  lobes  and  lobules  separated  and 
supported  by  white  fibrous  and  adipose  tissues.  All  of  the 
individual  glands  are  further  bound  together  in  the  same 


2.22 


THE   SKIN    AND    ITS    APPENDAGES. 


manner.     The  ducts  converge  and  end  in  the  nipple,  which 
forms  a  small  projecting  mass. 

Each  lobule  consists  of  a  number  of  acini,  which  are  tubu- 
lar or  alveolar  in  structure.  The  numiber  of  these  depends 
upon  the  state  of  activity.     In  the  gland  of  pregnancy,  the 


E^li# 


!;■  PC 


Fig.    82. — Section    op    Lactating    Human    Mammary    Gland     (Stohr's 

Histology), 
a.   Alveolo-tubule ;   6.   tubule ;   c.   duct ;   d.   connective  tissue. 

acini  are  very  numerous,  and  are  lined  by  simple  columnar, 
or  cuhoidal  cells,  in  which  are  accumulated  the  fat  globules 
that  form  the  important  constituent  of  the  milk.  These 
cells  rest  upon  a  basement  membrane,  but  in  places  are  sep- 
arated therefrom  by  peculiar  elements  called  basket  cells, 
which  are  compared  to  the  smooth  muscle  tissue  of  the  sweat 


MILK.  223 

glands.  The  ducts  are  lined  by  simple  columnar  cells  that 
rest  upon  a  basement  membrane,  outside  of  which  circular 
bundles  of  white  fibrous  tissue  are  to  be  found.  These 
ducts  unite  to  form  the  main  secretory  duct  of  the  individ- 
ual glands ;  each  m-ain  duct  dilates  to  form  a  small  ampulla, 
or  SINUS  LACTIFEROUS,  before  the  nipple  is  reached. 

The  nonlactating  gland  consists  chiefly  of  white  fibrous 
and  adipose  tissues,  in  which  are  seen  a  number  of  ducts, 
but  few  acini.  The  bulk  of  the  organ  consists  of  the  fibrous 
and  adipose  tissues.  When  pregnancy  occurs,  the  ducts 
divide  and  redivide,  and  the  terminal  portions  dilate  to  form 
the  acini.  This  increase  in  the  glandular  part  causes  the  in- 
crease in  the  size  of  the  organ,  and  the  tingling  sensation 
that  occurs  at  that  time. 

After  lactation  has  ceaised,  most  of  the  acini  undergo  retro- 
gression, atrophy,  and  disappear.  Some  of  the  ducts  under- 
go  the  same  change.  As  a  result,  the  gland  becomes  some- 
what smaller  and  flabby.  In  old  age,  or  after  the  child-bear- 
ing period  bas  passed,  the  glandular  and  ductular  portions 
retrograde  and  disappear  in  the  same  manner,  until,  in  old 
age,  they  may  be  entirely  absent.  The  glands  are  then  rep- 
resented by  fibrous  and  adipose  tissues. 

Milk  consists  of  minute  globules  of  fat,  o.i  to  0.5  mm.  in 
diameter,  surrounded  by  a  thin  layer  of  casein.  This  pre- 
vents them  from  coalescing.  They  are  formed  in  the  proto- 
plasm of  the  cells  of  the  acini,  but  the  cell,  after  discharging 
them,  does  not  die,  as  formerly  supposed.  At  first,  col- 
ostrum is  present  in  the  glands ;  this  consists  of  fat  and 
colostrum  corpuscles,  which  are  either  degenerated  gland 
cells,  or  leukocytes. 

The  nipple,  or  mammilla,  consists  of  an  outer  covering 
of  pigmented  skin,  and  within  it  the  individual  ducts  are 
found.     These  are  separated  from  one  another  by  fibrous 


224  THE   SKIN    AND    ITS    APPENDAGES. 

tissue  and  involuntary  nonstriated  muscle.  The  muscle  tis- 
sue is  arranged  circularly  and  vertically,  extending  to  the 
apex  of  the  mammilla.  By  its  contraction,  an  erection  is  pro- 
duced. Such  tissue  is  called  false  erectile  tissue.  At  the 
base  of  the  nipple  is  a  pigmented  area  called  the  areola, 
which  contains  a  ring  of  sebaceous  glands  called  the  glands 

OF  MONTGOMMERY. 

In  addition  to  the  general  blood-vessels,  the  various  ap- 
pendages have  special  supplies.  From  the  suhpapillary  ar- 
terial plexus,  branches  pass  to  the  hair  follicles,  to  form  one 
plexus  beneath  the  hyalin  membrane,  and  another  in  the 
papilla.  The  venous  radicals  formed,  empty  into  suhpapil- 
lary plexus  of  veins.  Around  the  sebaceous  and  sweat 
glands,  the  subpapilbry  arterial  plexus  forms  a  close  net- 
work of  capillaries,  which  form  venous  branches  that  empty 
into  the  suhpapillary  venous  plexus. 

The  blood-vessels  of  the  mammary  gland  converge  to- 
wards it,  and  pass  into  the  organ  in  the  partitions  between 
the  lobules.  From  these  vessels,  branches  extend  into  the 
lobules,  and  form  close  plexuses  around  the  acini. 

The  appendages  are  supplied  with  nerves  from  both  sym- 
pathetic and  cerebro-spinal  systems.  The  hair  follicles  re- 
ceive medullated  fibres  that  branch  freely,  and  end  in  spoon- 
shaped  masses  upon  the  glassy  membrane.  The  sweat-glands 
are  supplied  with  sympathetic  fibres,  that  form  a  close  net- 
work beneath  the  basement  membrane,  which  they  pierce,  to 
end  upon  the  gland  cells.  The  mammary  gland  has  both 
varieties  of  nerves.  The  sympathetic  are  the  more  numer- 
ous ;  these  pass  to  the  blood-vessels  on  the  one  hand,  and  to 
the  acini  on  the  other.  In  the  latter,  they  form  a  plexus 
beneath  the  basement  membrane,  and  from  this  plexus, 
branches  end  upon  the  gland  cells.  The  nerve-endings  in 
the  nipple  are  numerous. 


NERVES    OF    MAMMARY    GLAND.  225 

The  glands  and  hair  folHcles  are  surrounded  by  separate 
lymplmtic  plexuses  that  empty  into  the  subcutaneous  ves- 
sels. In  the  mammary  gland,  plexuses  are  found  between 
the  individual  lobes,  around  the  ampullae  and  in  the  nipple. 
These  empty  into  the  axillary  lymphatics. 


CHAPTER  XVII. 


THE  NERVOUS  SYSTEM. 

The  Nervous  System  consists  of  the  Cerebrum,  Cere- 
bellum, Pons,  Medulla  and  Spinal  Cord.  It  is  surrounded 
by  three  membranes,  the  Dura,  Arachnoid  and  Pia. 

The  Dura  is  a  tough  membrane  composed  of  interlacing 
bundles  of  white  fibrous  and  yellow  elastic  tissues  that  con- 
tain lymph  spaces  between  them.  Within  the  skull,  it  forms 
the  inner  periosteum  of  the  cranium,  which  relation  ceases 
at  the  foramen  magnum,  the  entrance  into  the  vertebral 
canal.  In  the  latter,  it  is  not.  connected  with  the  bone,  but- 
hangs  like  a  bag  and  contains  the  spinad  cord.  This  mem- 
brane is  lined  by  endothelial  cells,  and  forms  the  outer  boun- 
dry  of  the  subdural  lymph  space.  It  is  quite  vascular,  and 
a  few  nerves,  that  pass  to  the  blood  spaces,  are  found. 

The  Arachnoid  is  a  thin,  delicate  membrane  made  by 
loosely  interwoven  bundles  of  white  fibrous  tissue.  It  lies 
closely  applied  to  the  dura,  and  is  separated  from  the  pia  by 
the  SUBARACHNOIDEAN  LYMPH  SPACE.  This  space  is  also 
lined  by  endothelial  cells.  It  forms  the  Pacchionian 
BODIES  and  villi,  but  contains  neither  blood-vessels  nor 
nerves. 

The  Pia  is  the  vascular  membrane.  Its  outer  portion 
contains  the  bulk  of  the  vessels,  while  the  inner  enters  into 
close  relation  with  the  nervous  tissue.  Its  blood-vessels  lie 
in  the  fibro-elaistic  network,  surrounded  by  perivascular 
lymphatics.  Its  arachnoidean  surface  is  covered  by  endo- 
thelial cells.  Only  a  few  nerve  fibres  are  present.  The  pia 
is  the  only  one  of  these  membranes  that  follows  the  fissures 
and  depressions  of  the  nervous  system. 

The  Nervous  System  consists  of  Gray  and  White  Matter. 

226 


THE  CEREBRUM.  22/ 

The  Gray  Matter  consists  of  nerve  cells,  their  proces- 
ses and    NEUROGLIA. 

The  NERVE  cells  are  of  various  forms,  unipolar,  bipolar 
and  multipolar.  The  first  possess  but  one  process,  the  second, 
tzi^o,  and  the  third,  three  or  more.-  The  cell-body  may  be  of 
any  shape,  and  consists  of  granular  protoplasm  that  has  a 
fibrillar  structure.  The  nucleus  is  usually  large,  but  does 
not  take  a  deep  stain.  The  nucleolus  is  very  large,  and 
stains  deeply. 

The  PROCESSES  are  dendritic  and  axis  cylinder.  The 
DENDRITES  are  minor  processes  that  are  subdivided  into  a 
great  many  smaller  processes,  the  tele  dendrites.  The  axis- 
cylinder  process,  or  neurit,  is  the  main  process.  In  cells 
of  the  FIRST  TYPE,  or  Deiter  cells,  the  neurit  leaves  the  gray 
matter  to  become  the  center  of  a  nerve  fibre.  In  those  of 
the  SECOND  TYPE,  or  GoLGi  CELLS,  the  axis-cylinder  never 
leaves  the  gray  matter. 

The  NEUROGLIA  consists  of  neuroglia,  or  glia  cells,  and 
a  fibrillar  intercellular  substance.  The  cells  are  either  spider 
or  mossy.  For  a  detailed  description  of  these,  see  the  chapter 
on  Nervous  Tissues  (p.  79). 

The  White  Matter  consists  of  medullated  nerve  fibres 
held  together  by  neuroglia  and  white  fibrous  connective 
tissue. 

In  the  Cerebrum  and  Cerebellum,  the  Gray  Matter  is 
extenml,  and  constitutes  the  cortex.  The  White  Matter 
is  internal,  and  is  called  the  Medulla.  In  the  Spinal  Cord, 
the  Gray  Matter  is  surrounded  by  the  White  Matter. 
In  the  Medulla  and  Pons,  there  is  no  distinct  arrangement. 

CEREBRUM. 

Beside  the  Cerebrum,  there  are  other  masses  of  nervous 
tissue  to  be  considered  here.  These  are  the  Olfactory  Lobes, 
the  Pituitary  and  Pineal  Bodies. 


228 


THE   NERVOUS  SYSTEM. 


The  GRAY  MATTER,  or  Cortcx  of  the  Cerebrum,  is  divided 
into  layers  that  are  not  sharply  limited  from  one  another.   In 


or-j 


V 


1% 


\.y. 


FIG.  83. — Vertical  Section  of  Human  Cerebral  Cortex. 

a.  Pia  mater  ;  h.  molecular  layer  ;  c.  small  pyramidal  cells ;  d.  large  pyra- 
'mydal  cells;  e.  layer  of  polymorphous  cells;  f.  layer  Oi.  fusiform  cells; 
g.  medulla ;   In.  radial  bundles  of  medullated  fibres  in   cortex ;   i.  pial 
process  ;  fc.  large  pyramidal  cell. 

some  regions,  five  can  be  nrade  out,  in  others  three,  while 
four  form  the  average  number.  The  Cortex  is  made  irregu- 
lar  by   the   formation   of   fissures   and   convolutions.      The 


THE   CEREBRUM.  229 

latter  consist  of  a  central  mass  of  white  matter,  Medulla, 
covered  by  the  gray  matter,  or  cortex. 

The    CORTICAL    LAYERS    are,    from    without   inward,    the 

MOLECULAR,  SMALL  PYRAMIDAL,  LARGE  PYRAMIDAL  and 
MIXED,  or  POLYMORPHOUS  LAYERS. 

The  MOLECULAR  layer  consists  mainly  of  neuroglia  and 
cell-processes.  The  latter  are  derived  from  the  next  two 
layers,  and  are  chiefly  dendrites.  The  neuroglia  forms  a 
network  within  which  the  dendrites  and  medullated  nerve 
fibres  lie.  The  latter  run  parallel  to  the  surface,  and  are 
therefore  called  tangential  fibres. 

Among  the  cellular  elements  are  some  of  the  second  type, 
or  Golgi  cells.  The  nms-cylinders  of  these  cells  remain  in 
the  gray  matter.  They  are  polygonal,  stellate  and  spindle- 
shaped  cells,  in  which  the  dendrites  run  parallel  to  the  sur- 
face, and  are  called  the  cells  of  Cajal. 

The  LAYER  OF  SMALL  PYRAMIDAL  cclls  is  composcd  of  Sev- 
eral layers  of  cells,  the  dendrites  of  which  extend  into  the 
molecular  layer,  while  some  of  the  axis  cylinders  partially 
pass  to  the  molecular  layer  (second  type)  and  others  pass 
into  the  medulk)  (first  type,  or  Deiter  cell).  In  the  latter 
case,  the  axis  cylinders  give  off  branches  called  collaterals 
The  CELLS  themselves  are  small,  measuring  lo  to  12  microns 
in  diameter,  and  triangular  in  outline.  The  dendrites  arise 
from  the  angles,  while  the  axis-cylinder,  or  neurit,  has  its 
origin  at  the  middle  of  the  base. 

The     LAYER    OF     LARGE     PYRAMIDAL     Cclls     COUStitutCS     the 

widest  and  most  important  layer.  The  cells  are  usually  20 
to  50  microns  in  diameter,  though  some  may  exceed  this. 
The  dendrites  pass  to  the  molecular  layer,  while  the  neurit 
becomes  a  medullated  nerve  fibre.  These  cells  are,  therefore, 
cells  of  the  first  type.  Their  outline  is  triangular,  and  the 
nucleus  is  large  and  prominent. 


230  THE   NERVOUS  SYSTEM. 

The  LAYER  OF  POLYMORPHOUS  cells  coiitaiiis  cells  of  vari- 
ous shapes ;  these  are  large  and  small  pyramidal,  spindle- 
shaped,  oval  and  polygonal.  The  latter  predominate.  The 
DENDRITES  pass  to  the  upper  layers  of  the  cortex,  while  the 
AXIS-CYLINDERS,  in  some  instances,  remain  in  the  cortex,  and 
in  others  pass  into  the  medulla. 

In  the  last  three  layers,  bundles  of  medullated  nerve 
fibres,  having  a  radial  course,  are  seen.  They  begin  in  the 
small  pyramidal  layer,  increase  in  number  as  they  approach 
the  medulla,  and  contain,  beside  those  fibres  derived  from 
the  immediate  cortical  cells,  others  whose  origin  is  not 
definite. 

The  Medulla  consists  of  medullated  nerve  fibres  from 
various  sources ;  those  that  pass  to  the  periphery  of  the  body 
from  the  pyramidal  and  polymorphous  cells ;  others  from  the 
pyramidal  cells  that  pass  from  one  hemisphere  to  the  other ; 
those  that  connect  different  areas  of  the  same  side  (pyra- 
midal cells),  and  whose  axis  cylinders  are  "T"  branched, 
and  pass  into  the  cortex  sooner  .or  later ;  lastly,  fibres  that 
come  from  distant  parts  of  the  same  or  the  other  hemisphere, 
or  other  parts  of  the  nervous  system. 

OLFACTORY  LOBE. 

The  Olfactory  Lobe,  that  portion  of  the  nervous  system 
devoted  to  the  sense  of  smell,  is  comparatively  small  in  mati. 
There  are  Uve  layers  present,  which  are  best  marked  in  the 
central  part  of  the  organ.  These  are  the  layer  of  peripher- 
al FIBRES,  the  glomerular  layer,  the  molecular  layer, 
the  LAYER  OF  mitral  CELLS  and  the  granule  layer. 

The  layer  of  peripheral  fibres  consists  of  a  plexus 
formed  by  the  fibres  of  the  olfactory  nerve. 

The  glomerular  layer  lies  beneath  the  above,  and  is 
made   up   of   peculiar   round,   or   oval,   bodies    100   to   300 


THE    PITUITARY    BODY.  23 T 

microns  in  diameter.     They  are  said  to  be  masses  of  inter- 
lacing tclodendria  of  the  olfactory  and  mitral  cells. 

The  MOLECULAR  LAYER  is  made  up  of  large  and  small 
spindle-shaped  ganglion  cells  whose  dendrites  end  in  the 
glomeruli,  and  whose  axis-cylinders  pass  to  the  fifth,  or 

GRANULAR,  LAYER. 

The  LAYER  OF  MITRAL  CELLS  consists  mainly  of  large 
pyramidal  cells  varying  in  size  from  30  to  50  microns. 
Their  dendrites  pass  to  the  glomeruli  and  the  axis-cylinders 
to  the  granule  layer. 

The  GRANULE  LAYER  consists  of  uervc  cells  and  fibres. 
The  cells  are  stellate  ganglion  elements,  and  peculiar  gran- 
ule cells ;  the  latter  appear  to  have  no  axis-cylinders. 
Some  of  the  nerve  fibres  are  derive.d  from  the  mitral  cells, 
some  from  the  molecular  layer,  and  others  from  the  outside. 
The  deeper  bundles  enclose  granule  and  stellate  cells. 

THE  PITUITARY  BODY. 

The  Pituitary  Body,  or  Hypophysis,  is  a  small  organ 
consisting  of  a  nervous,  or  posterior  lobe,  and  an  epithel- 
ial, or  ANTERIOR  LOBE.  Both  are  surrounded  by  a  common 
capsule  of  fibrous  tissue. 

Although  the  posterior  lobe  has  a  nervous  origin,  its 
structure,  in  man,  in  no  way  resembles  that  of  the  ner\ous 
system.  Fibrous  tissue  predominates,  a'nd  the  spindle-shaped 
cells  are  comparatively  few  and  pigmented.  The  anterior 
lobe,  however,  is  divided  into  a  number  of  tubular  alveoli, 
lined  by  polygonal  epithelial  cells.  These  cells  are  of  two 
varieties,  acidophilic  and  basophilic ;  the  latter  are  the  more 
numerous.  These  are  irregularly  arranged  so  that  a  small 
lumen  remains.  This  may  contain  colloid  substance.  The 
nuclei  are  large  and  oval.  The  interstitial  tissue  in  both 
lobes  is  quite  vascular. 


232  THE   NERVOUS  SYSTEM: 

THE  PINEAL  BODY. 

The  Pineal  Body,  or  Epiphysis,  is  a  small,  apparently  un- 
important organ  in  man.  In  some  lower  animals,  it  is  a 
visual  organ.  This  rudimentary  structure  consists  of  a 
number  of  tubules  lined  by  polygonal  cells  supported  by 
fibrous  tissue  and  neuroglia  in  the  lower  part.  These 
tubules  contain  the  brain  sand,  or  acervulus  cerebri,  pe- 
culiar concretions  of  phosphate  and  carbonate  of  magnesium, 
ammonium  and  calcium,  which  are  not  limited  to  this  body, 
however,  but  may  be  found  in  other  portions  of  the  nervous 
system. 

CEREBELLUM. 

The  Cerebellum,  or'  Little  Brain,  has  a  characteristic 
gross  appearance,  when  sectioned.  Its  Cortex  and  Medulla 
are  so  colored  and  arranged  as  to  give  the  appearance  of 
a  TREE,  called  the  arbor  vitae,  or  tree  of  life. 

The  Cortex  consists  of  three  sharply-marked  layers,  the 

MOLECULAR,     the    GANGLIONIC    and    GRANULE    LAYERS,     from 

without  inward. 

The  MOLECULAR  LAYER  consists  of  a  network  of  neuroglia, 
in  which  the  dendritic  branches  of  the  cells  of  the  lower 
layers  are  found.  They  are  mostly  those  of  the  ganglionic 
CELLS.  In  addition,  there  are  small  and  large  multipolar 
cells ;  the  axis  cylinders  of  the  former  remain  in  this  layer, 
while  those  of  the  latter  pass  toward  the  second  layer  and 
form  a  network  of  branches  around  the  ganglionic  cells. 
They  are  thereupon  called  the  basket  cells.  Fibres  from 
the  MEDULLA  pass  into  this  layer  and  break  into  a  great 
number  of  delicate  terminal  twigs. 

The  GANGLIONIC  LAYER,   Or  LAYER  OF  PuRKINJE  CELLS,    is 

very  characteristic.     The  bodies  of  these  cells  are  very  big, 
measuring  30  to  70  microns.    A  large  nucleus  and  a  distinct 


THE  CEREBELLUM, 


^?>?> 


nucleolus  are  present.  The  protoplasm  is  fibrillar,  but  con- 
tains no  pigment  granules.  Two  main  processes  extend 
from  the  body ;  the  lower,  or  neurit,  passes  to  the  medulla 


...y 


^—  ' 


Fig.  84. — Vertical  Section  of  the  Human  Cerebellum. 
A.  Cerebellum,   low  power  ;   B.   cerebellum  highly  magnified ;   a.  molecular 
and  ganglionic    layers ;    ft.   granule   layer ;    c.   medulla ;   d.   pia   matter ; 
e.  cell  of  Purkinje ;   f.  cell  of  molecular  layer ;  g.   cells  of  the  granule 
layer ;   C.   Cell  of  Purkinje. 


and  becomes  a  medullated  nerve  fibre.  The  upper,  or  den- 
dritic, quickly  breaks  into  two,  that  run  at  right  angles 
to  the  main   stem.     From   the  upper   sides  of   these   two 


234  THE   NERVOUS  SYSTEM. 

branches,  an  immense  number  of  small,  delicate  branches 
are  formed.  These  cells  are  called  antler  cells,  from  their 
appearance.  The  cells  are  more  numerous  at  the  top  than  at 
the  bottom  of  the  convolutions. 

The  GRANULE  LAYER  is  composed  of  great  and  small 
GRANULE  CELLS.  The  SMALL  cells  possess  large  nuclei  and  a 
small  amount  of  protoplasm.  The  dendritic  processes  re- 
main mostly  in  this  layer,  while  the  neurit  passes  to 
the  molecular  layer,  forming  ''T"  branches  that  run 
parallel  to  the  surface.  The  larger  cells  resemble  the  cells 
of  the  ganglionic  layer,  but  the  axis-cylinder  forms  a  net- 
work of  branches,  being  a  cell  of  the  second  type.  Beside 
the  neuroglia  present,  there  are  some  fibres  of  the  medullated 
variety.  This  layer  is  thicker  at  the  summit  of  the  convolu- 
tion, and  diminishes  as  the  base  is  reached. 

The  Medulla  consists  of  medullated  nerve  fibres,  support- 
ed by  neuroglia  and  connective  tissue ;  of  these  fibres,  some 
form  the  inferior  peduncles;  others  the  middle  ( pontine )y 
and  the  remainder  the  superior  peduncles,  which  connect  the 
cerebellum  with  the  corpora  quadrigemina. 

THE  PONS. 

The  Pons  has  not  the  definite  arrangement  of  the  cere- 
brum or  spinal  cord.  Its  nerve  fibres  are  collected  into  large 
bundles,  and  the  gray  matter  is  found  in  masses  called 
nuclei.    It  is  divided  into  ventral  and  dorsal  portions. 

The  VENTRAL  part  is  made  up  chiefly  of  iransverse  fibres 
that  connect  the  cerebellar  hemispheres ;  to  these  are  added 
certain  fibres  that  pass  from  the  cerebral  cortex  to  the  me- 
dulla (anterior  pyramids).  These  transverse  fibres  are  sub- 
divided into  a  venlral,  or  superficial;  dorsal,  or  deep;  and 
middle,  or  penetrating  layers.  The  pyramidal  fibres  lie  in 
two  groups,  one  on  each  side  of  the  midline,  as  they  pass 


THE   MEDULLA.  235 

towards  the  cerebrum  from  the  lower  part  of  the  pons,  these 
pyramids  becomie  separated  into  numerous  bundles  by  the 
penetrating  transverse,  or  middle  fibres.  In  the  spaces  be- 
tween the  fibres,  is  found  gray  matter  composed  of  small 
multipolar  ganglion  cells. 

The  DORSAL  portion  of  the  pons  consists  of  the  continua- 
tion of  the  dorsal  tracts  of  gray  matter,  and  the  formatio 
reticularis.  The  latter  consists  of  fibres  that  form  a  coarse 
network  in  which  gray  matter  is  distributed. 

The  upper  portion  of  the  fourth  ventricle  is  within  the 
pons.  Its  floor  is  covered  by  a  layer  of  gray  matter,  and 
here  certain  nerves  (fifth,  sixth,  seventh  and  eighth)  have 
their  origin.  Here  also  are  found  nerve  cells  whose  pig- 
mentation and  grouping  make  them  visible  to  the  naked 
eye. 

THE  MEDULLA. 

The  Medulla  connects  the  central  system  with  the  spinal 
cord.  It  resembles  the  cord  more  than  other  portions,  and 
consists  of  the  continuation  of  its  tracts  and  gray  matter, 
though  somewhat  dififerently  arranged. 

Most  of  the  motor  fibres,  as  they  pass  to  the  spinal  cord, 
dcciissaie,  or  cross  to  the  opposite  side  from  which  they 
originate.  This  decussation  occurs  in  the  medulla,  and  is 
the  cause  of  the  derangement  of  the  gray  matter,  especially 
of  the  ventral  horns. 

The    GRAY    MATTER    COUsistS    of    the    VENTRAL    and    DORSAL 

HORNS.  The  decussating  fibres,  in  passing  to  the  opposite 
side,  take  an  oblique  course ;  in  so  doing,  they  cut  the  horns 
of  gray  matter  so  that  the  ventral  mass  becomes  separated 
from  the  basal  portion.  The  former  is  pushed  to  the  side 
and  dorsally,  by  these  fibres,  thereby  forming  the  olivary 
BODIES.  This  mass  of  gray  matter  is  now  called  the  lateral 
NUCLEUS.    The  BASAL  portion  of  the  horns  lies  as  a  nucleus 


236  THE  NERVOUS  SYSTEM. 

by  the  side  of  the  central  canal.  The  transverse  and  longi- 
tudinal fibres  entering  the  medulla  form  a  loose  network,  the 
FORMATio  RETICULARIS,  which  is  filled  with  gray  matter. 

The  DORSAL  columns  of  white  matter  (Goll  and  BuR- 
dach),  increasing  in  size  by  the  addition  of  two  gray  masses, 
affect  the  dorsal  horns  of  gray  matter,  gradually  forcing 
these  nearer  to  the  ventral  horns.  These  gray  masses  re- 
ferred to  are  the  nucleus  gracilis  and  the  nucleus  cun- 
EATUS.  It  is  in  these  nuclei  that  the  fibres  of  the  dorsal  col- 
umns end.  The  nerve  cells  in  these  nuclei  send  their  axis 
cylinders  to  the  cerebellum  of  the  same  and  opposite  sides, 
and  to  higher  portions.  The  latter  fibres  constitute  the  in- 
ternal ARCUATE  FIBRES.  They  are  sensory,  and  form  a 
second  decussation  above  that  of  the  motor  fibres.  The  in- 
ternal ARCUATE  FIBRES  pass  to  the  ccrebrum,  and  in  passing 
to  their  destination,  have  a  longitudinal  course.  The  fibres 
that  pass  to  the  cerebellum  are  seen  ventrally  in  relation  to 
anterior  pyramids,  and  enter  into  the  inferior  peduncles  of 
the  cerebellum.  These  form  the  anterior  external  arcu- 
ate FIBRES.  Fibres  from  the  posterior  funiculi  also  enter 
these  peduncles,  and  they  constitute  the  posterior  internal 

FIBRES. 

The  INFERIOR  OLIVARY  BODY  COUtaiuS  the  DENTATE  NU- 
CLEUS. This  consists  of  an  irregular  band  of  gray  matter 
open  toward  the  midline,  at  which  place  the  fibres  enter  and 
leave.  These  fibres  are  the  olivary  peduncles,  which  pa'ss 
through  the  gray  matter  and  then  through  the  restiform 
bodies  to  the  cerebellum.  Near  this  gray  mass  are  found 
two  other  collections  of  gray  matter,  the  outer  dorsal  and 
the  INNER  (mesial)  accessory  olivary  nuclei. 

The  medulla  contains  the  lower  half  of  the  fourth  ven- 
tricle. In  the  gray  matter  of  its  floor,  is  a  collection  of 
ganglion  cells,  the  hypoglossal  nucleus,  which  is  the  point 


THE    SPINAL    CORD.  237 

of  origin  of  the  hypoglossal  nerve.  Near  this  collection, 
and  at  first  dorsal,  then  lateral,  is  a  collection  constituting 
the  NUCLEUS  of  the  tenth  and  ninth  nerves. 

The  ANTERIOR  PYRAMID  of  the  medulla  is  made  up  of  the 
fibres  of  the  direct  pyramidal  tract  of  the  cord,  and  also  some 
of  the  fibres  from'  the  cross  pyramidal  tract. 

The  LATERAL  TRACT  consists  of  fibres  of  the  ground  bundle, 
and  fibres  not  included  in  the  direct  cerebellar  and  cross 
pyramidal  tracts.  The  former  enter  into  the  formation  of 
the  formatio  reticularis,  while  the  sensory  -fibres  continue  to 
the  cerebrum. 

The    RESTIFORM    BODIES,    Or    INFERIOR    PEDUNCLES    of    the 

cerebellum,  contain  fibres  from  the  medulla  and  cord,  and 
some  from  the  pons. 

The  POSTERIOR  PYRAMIDAL  TRACT  is  formed  by  the  con- 
tinuation of  the  dorsal  columns  of  the  cord. 

THE  SPINAL  CORD. 

This  portion  of  the  nervous  system  is  the  longest.  It  is 
characterized  by  possessing  the  gray  matter  internally  and 
the  white  matter  externally.  Its  form  varies  in  the  different 
regions ;  in  the  cervical  and  lumbar  areas,  it  is  enlarged,  and 
these  enlargements  are  termed  the  intumescentia  cervi- 
CALis  and  lumbalis,  respectively.  The  outline  in  the  cer- 
vical region  is  oval,  in  the  thoracic  region  almost  circular, 
and  in  the  lumbar  portion  oval. 

The  cord  ends  in  the  neighborhood  of  the  second  lumbar 
vertebra,  and  its  termination  is  cone-shaped.  This  is  called 
the  CONUS  medullaris.  Owing  to  the  fact  that  the  cord  is 
shorter  than  the  vertebral  canal,  the  lower  lumbar,  the  sacral 
and  coccygeal  nerves  pass  down  for  varying  distances  be- 
fore reaching  their  respective  foramina.  This  produces 
a  mass  of  fibres,  in  the  lower  part  of  the  canal,  called  the 


238  THE   NERVOUS  SYSTEM. 

CAUDA  EQUINA.  In  the  center  of  the  latter  is  a  fibrous  band 
that  extends  toward  the  end  of  the  canal.     It  is  the  filum 

TERMINALE. 

The  Cord  consists  of  two  hemispheres  separated  ve-ntrally 
by  the  anterior,  or  ventral  median  fissure,  in  which  is 
seen  a  process  of  the  pia.  Dorsally,  no  fissure  exists,  but  a 
septum  is  present.  This  is  the  posterior,  or  dorsal  medi- 
um   SEPTUM,   or   raphe. 

The  gray  matter  of  the  cord  is  arranged  in  the  form  of 
a  letter  H,  the  two  side  bars  constituting  the  horns,  and 
the  cross-bar  the  gray,  or  posterior  commissure.  The 
horns  are  further  subdivided  into  ventral,  or  anterior, 
and  DORSAL,  or  posterior. 

The  VENTRAL  HORNS  are  large  and  blunt,  and  do  not  ex- 
tend to  the  periphery.  In  them  are  found  collections  of 
lairge,  multipolar  ganglion  cells  having  a  motor  function. 
The  axis-cylinders  of  these  cells  pass  out  of  the  ventral 
portion  of  the  cord  as  the  ventral  root  of  the  spinal 
NERVE.  These  cells  average  60  to  120  microns,  and  are 
quite  numerous.  Each  is  surrounded  by  a  distinct  lymph 
space.     They  are  collected  into  three  groups,  antero-med- 

lAN,   ANTERO-LATERAL   and   POSTERO-LATERAL.       Those    of   the 

ANTERO-MEDiAN  group  do  not  cxist  in  the  lumbar  region 
w^hile  the  postero-lateral  cells  are  present  only  in  those 
portions  of  the  cord  that  are  well  developed. 

The  DORSAL,  or  posterior  horns  are  sharp  amd  pointed, 
and  usually  extend  to  the  edge  of  the  cord.  The  cells  here 
are  small  in  number  and  size,  averaging  from  15  to  20  mi- 
crons, and  are  scattered  along  the  external  margin.  They 
comprise  marginal  cells  whose  axis  cylinders  pass  into  the 
lateral  columns  after  passing  through  the  substantia  gelatin- 
osa ;  spindle-shaped  cells,  the  neurits  of  which  pass  into  the 
dorsal  columns;  stellate  cells,  the  axis  cylinders  of  which 
pass  into  the  dorsal  columns  of  Burdach. 


THE    SPINAL    CORD. 


239 


II  TO 


Fig.    85. — Cross-section    of    Human    Spinal    Cord    at   Lower    Cervical 
Region.      From    Decapitated    Criminal    (Dr.    H.    H.    Cushing). 

1.  Anterior  spinal  artery :  2.  pial  process  in  ventral  fissure :  3.  dura ; 
4.  nerve  fibres  from  ventral  horn  (motor  root  fibres)  ;  5.  stellate 
cells  of  ventral  Jiorn  ;  6.  ventral  horn  :  7.  dorsal  horn :  8.  nerve 
fibres  to  dorsal  horn  (sensory  root  fibres)  :  9.  dorsal  septum;  10.  dor- 
sal spinal  artery  and  vein  (arteria  et  vena  fissurae  posterioris)  : 
n.  fibres  of  the  column  of  Goll  ;  12.  tissue  separating  the  columns  of 
Goll  and  Purdach  :  1.^.  column  of  Burdach  ;  14.  traces  of  tLe  lateral 
horn:  15.  fibres  of  the  lateral  columns:  17.  central  canal  in  the  gray 
comm  ssure :  18.  ventral,  or  white  commissure:  19.  fibres  of  the 
ventral    columns  :  20.  arteria  et   vena  fissurae   anterioris. 


240  THE   NERVOUS  SYSTEM. 

Along  the  median  edge  of  the  horn,  near  its  junction  with 
the  gray  commissure,  lies  a  group  of  cells  that  expends  from 
the  cervical  to  the  mid-lumbar  region.  This  is  the  vesicular 
COLUMN  OF  Clark.  A  similar  collection,  though  less  dis- 
tinct, is  seen  in  the  lower  lumbar  region,  the  nucleus  of 
Stilling. 

The  neurits  of  these  cells  of  the  dorsal  horns  pass  into 
the  DORSAL  columns;  those  of  the  vesicular  column  of 
Clark  pass  into  the  direct  cerebellar  tract,  on  the  same 
side  and  into  the  ventral  (anterior)  commissure.  In  the 
dorsal  horn  is  the  substantia  gelatinosa  Rolandi,  which 
consists  of  cells  of  the  second  type  (Golgi). 

The  GRAY  COMMISSURE  consists  of  medullated  and  non- 
medullated  commissural  fibres  separated  into  ventral 
(smaller)  and  dorsal  (larger)  bands  by  the  central  canal 
of  the  cord.  The  ventral  portion  is  called  the  ventral,  or 
anterior  gray  COMMISSURE,  while  the  other  receives  the 
name  of  dorsal,  or  posterior  gray  commissure.  The  whole 
is  the  GRAY,  or  posterior  commissure,  in  contradistinction 
to  the  anterior,  or  white  commissure. 

The  CANAL  of  the  cord  is  the  remains  of  the  embryonal 
cavity  within  this  portion  of  the  nervous  system.  In  child- 
hood, it  is  lined  by  simple  ciliated  elements,  the  ependymal 
CELLS.  Above,  it  communicates  with  the  fourth  ventricle, 
and  its  form  varies  in  the  different  portions  of  the  cord.  It 
becomes  more  or  less  obliterated  with  increasing  age,  par- 
tially by  increased  growth  of  the  lining  ependymal  cells  and 
partially  by  the  ingrowth  of  neurogliar  processes. 

Besides  the  nerve  cells,  processes  and  fibres,  the  gray 
matter  contains  that  peculiar  supportive  tissue  found  only 
in  the  nervous  system,  called  neuroglia.  This  substance  is 
ectodermal  in  origin. 


THE    SPINAL    CORD.  24I 

Neuroglia  consists  of  two  varieties  of  cells,  spider  and 
MOSSY.  The  spider  cells  are  composed  of  thin,  flat  bodies 
from  which  extend  large  slender  processes.  The  mossy 
cells  have  short,  heavy  processes.  In  addition  to  these, 
there  are  some  cells  that  possess  large  bodies  and  few  pro- 
cesses. Fibres  that,  apparently,  have  no  connection  with 
any  cell,  are  seen  passing  over  or  under  cell  bodies.  These 
processes  all  interlace  to  form  a  network  for  the  support  of 
the  nerve  cells  and  their  processes.  This  substance  is  the 
SUBSTANTIA  SPONGIOSA.  Around  the  central  canal  of  the 
cord,  the  substantia  spongiosis  becomes  more  modified,  and 
is  called  the  substantia  gelatinosa  centralis.  The  net- 
work is  much  closer  in  this  region.  Around  the  dorsal  horns, 
it  forms  a  homogeneous,  striated  mass,  in  which  a  few  nerve 
cells  are  found.     This  is  the  substantia  gelatinosa  Ro- 

LANDI. 

The  WHITE  MATTER  cousists  of  mcdullatcd  nerve  fibres, 
connective  tissue,  and  neuroglia.  Spider  cells  are  especially 
numerous  here.  The  nerve  fibres  possess  no  neurilemma, 
and  are  grouped  into  columns.  Ventrally,  they  aire  separated 
by  the  fissure,  and  dorsally,  by  the  septum,  into  the  hemi- 
spheres. Ventrally,  they  are  connected  by  a  band  of  white 
matter  that  lies  between  the  bottom  of  the  fissure  and  the 
gray  commissure.  This  is  the  white,  or  ventral  (anter- 
ior) commissure.  The  motor  fibres  are  usually  large,  meas- 
uring 15  to  20  microns  in  diameter.  The  sensory  are 
smaller. 

The  columns  are  as  follows : 

The  ventro-medium  columns  that  lie  between  the  ventro- 
median  fissure  and  the  ventral  roots  of  the  spinal  nerves ; 
the  LATERAL,  that  lie  between  the  ventral  and  dorsal  roots, 
and  are  subdivided  into  antero-lateral,  or  those  ventral  to 
the  transverse  midline,  and  the  postero-lateral,  or  those 
q 


242  THE  NERVOUS  SYSTEM. 

behind  the  same  line.  The  dorso-median  columns  that  lie 
between  the  septum  and  the  dorsal  roots  of  the  spinal  nerves. 
These  areas  are  further  subdivided  into  individual  columns. 
In  the  VENTRO-MEDiAN  region,  there  are  several  groups,  the 
DIRECT  PYRAMIDAL  TRACT  (Turck).  This  is  a  uarrow  band 
of  fibres  that  lies  along  the  fissure,  and  represents  the  non- 
decussating  fibres  from  the  motor  regions  of  the  brain.  The 
remainder  of  this  region  constitutes  the  anterior  ground 

BUNDLE. 

Along  the  periphery  of  the  ventro-lateral  region  is  a 
narrow  column  called  the  tract  of  Gower,  or  the  ascend- 
ing antero-lateral  tract.  Next  to  the  gray  matter  in 
the  entire  lateral  region  is  the  mixed  lateral  column;  this 
contains  both  motor  and  sensory  fibres.  Between  these  two 
lies  the  descending  antero-lateral  columiu,  or  lateral 

GROUND  bundle. 

In  the  postero-lateral  region,  along  the  periphery,  is 
the  DIRECT  cerebellar  tract.  This  is  composed  of  fibres 
derived  from  the  vesicular  columns  of  Clark.  Just  within 
this  is  the  large  crossed  pyramidal  tract,  which  consists 
of  the  motor  fibres  that  decussated  in  the  medulla.  Just  in 
front  of  the  dorsal  roots  is  a  smiaill  tract,  made  up  of  fibres 
from  the  posterior  roots,  the  bundle  of  Lissauer. 

The  dorso-median  region  consists  of  two  columns,  the 
column  of  Burdach,  funiculus  cuneatus,  and  the  col- 
umn OF  GOLL,  FUNICULUS  GRACILIS.      The  COLUMN  OF  BUR- 

dach  lies  next  to  the  gray  matter  of  the  dorsal  horn,  and  is 
the  outer  of  the  columns.  The  column  of  Goll  lies  along  the 
septum,  and  usually  does  not  extend  in  to  the  gray  commis- 
sure. These  columns  consist  of  sensory  fibres  that  pass  up  to 
the  brain,  and  also  of  short  fibres  that  connect  the  various 
segments  of  the  cord.  Capping  the  dorsal  root  is  a  collection 
of  nerve  fibres  from  the  lateral  part  of  the  dorsal  root.  This 


THE    SPINAL    CORD.  243 

is  the  COLUMN  of  Lissauer.  The  cells  of  these  fibres  all 
lie  in  the  spinal  ganglia,  and  the  fibres  pass  to  the  higher 
levels  of  the  cord. 

The  SPINAL  NERVES  consist  of  VENTRAL,  OT  MOTOR,  and 
DORSAL,  or  SENSORY  ROOTS.  Before  these  unite  to  form  the 
nerve,  a  mass  of  gray  matter  is  seen  upon  the  dorsal  root. 
This  is  the  spinal  ganglion.  The  fibres  of  the  dorsal  root 
are  derived  from  the  cells  that  lie  in  the  ganglia,  and  where 
they  enter  the  cord,  a  distinct  depression  is  noted.  The  ven- 
tral ROOT  is  made  up  of  fibres  derived  from  the  cells  in  the 
ventral  horn,  and  where  they  emerge,  only  a  slight  incurving 
of  the  surface  is  seen. 

The  circulaiion  of  the  nervous  system  is  carried  on  chiefly 
by  the  vessels  in  the  pia.  In  the  cerebrum,  the  vessels  of 
the  cortex  enter  vertically,  and  form  a  close  plexus  of  capil- 
laries most  plentiful  where  the  cells  are.  Those  intended 
for  the  medulla  are  larger,  and,  passing  through  the  cortex, 
form  capillary  networks  between  the  fibres  and  parallel  to 
them. 

In  the  CEREBELLUM,  the  capillaries  are  few  in  the  outer 
portion  of  the  molecular  layer,  but  in  the  granule  layer  and 
around  the  cells  of  Purkinje,  close  meshes  are  formed. 

In  the  spinal  cord,  there  are  two  sets  of  vessels,  those 
that  enter  at  all  points  of  the  periphery  and  supply  chiefly 
the  white  matter,  and  those  derived  from  the  artery  lying 
in  the  ventro-median  fissure ;  the  latter  set  goes  to  the  gray 
matter.  The  smaller  peripheral  vessels  remain  in  the  white 
matter,  and  run  parallel  to  the  fibres,  while  the  larger  pene- 
trate the  gray  matter  and  supply  the  outer  part.  The  artery 
in  the  fissure  sends  branches  into  the  gray  commissure;  these 
divide  right  and  left,  and  form  dense  plexuses  in  the  gray 
substance. 


244  THE   NERVOUS  SYSTEM. 

The  blood  is  collected  by  venous  radicals  that  have  the 
same   general  course. 

The  SUBARACHNOIDEAN  LYMPH  SPACE  continues  as  the 
PERIVASCULAR  LYMPHATICS  that  accompauy  the  blood- 
vessels. 


CHAPTER  XVIII. 


THE  EYEBALL  AND  LACRIMAL 
SYSTEM. 

The  Eyeball  is  one  of  the  most  important  organs  of  the 
special  senses.  It  is  composed  of  three  coats,  and  contains 
FOUR  REFRACTIVE  MEDIA.  The  COATS  are  the  External,  or 
Corneo-scleral ;  the  Middle,  or  Choroid,  Ciliary  Body  and 
Iris ;  and  the  Internal,  or  Retina. 

The  REFRACTIVE  MEDIA  are  the  cornea,  the  aqueous  and 
VITREOUS  HUMORS  and  the  lens.  Of  these,  the  cornea  and 
lens  alone  are  of  importance. 

The  Corneo-sclera  is  the  protective  and  transparent  coat 
of  the  eyeball. 

The  Sclera  constitutes  about  five-sixths  of  this  coat.  It 
is  composed  of  coarse  bundles  of  white  fibrous  tissue  that 
interlace  to  form  a  dense,  tough  coat.  These  bundles  are 
arranged  chiefly  longitudinally  and  transversely.  Between 
the  bundles  are  spaces  that  contain  large,  stellate  cells.  These 
spaces  communicate  with  the  lymph  spaces  within  the  cornea. 
On  its  external  surface,  the  sclera  is  in  relation  with  the 
CAPSULE  OF  Tenon,  and,  anteriorly,  the  conjunctiva.  To  it 
are  attached  the  ocular  muscles. 

Between  the  sclera  and  choroid  is  ai  lymph  space  called 
the  SUBSCLERAL  SPACE.  Here  the  tissue  is  loosely  arranged 
and  lined  by  endothelial  cells.  At  the  entrance  of  the  optic 
nerve,  the  sclera  is  pierced  by  the  nerve  fibres  so  as  to  form 
a  sieve-like  area,  the  lamina  cribrosa.  Pigmentation  oc- 
curs here,  as  well  as  at  the  corneo-scleral  junction.  Its  pres- 
ence in  the  subscleral  tissue  gives  rise  to  the  lamina  fusca. 

The  Cornea  is  a  specialized  portion  of  the  sclera  modified 
for  the  transmission  of  light.     It  consists  of  five  layers  : 

245 


246  THE  EYEBALL   AND  LACRIMAL   SYSTEM. 

ANTERIOR  EPITHELIUM,,  ANTERIOR  LIMITING  MEMBRANE, 
SUBSTANTIA  PROPRIA,  POSTERIOR  LIMITING  MEMBRANE,  and, 
POSTERIOR  ENDOTHELIUM. 

The  ANTERIOR  EPITHELIUM  is  a  Continuation  of  the  epi- 
thehum  of  the  conjunctiva.  This  is  of  the  stratified  squam- 
ous variety,  and  the  tunica  propria  beneath  is  not  papilla  ted. 
The  layers  of  cells  are  more  numerous  at  the  corneo-scleral 
junction  thao  in  the  center.  The  basal  cells  are  long  and 
columnar,  and  possess  processes  that  extend  into  the  an- 
terior elastic  lamina,  while  the  external  cells  are  squamous. 
The  middle  layers  are  prickle-cells,  and  the  spaces  between 
are  lymph  channels. 

The  ANTERIOR  ELASTIC  LAMINA,  Or  BOWMANS  MEM- 
BRANE, is  a  clear,  prominent  bamd  serving  as  a  basement 
membrane  to  the  epithelial  cells.  Although  called  elastic, 
it  does  not  consi'st  of  elastic  tissue.  It  is  thickest  in  the 
center,  and  becomes  thinner  as  the  junction  is  approached, 
where  it  disappears  entirely. 

The  SUBSTANTIA  PROPRIA  forms  the  bulk  of  the  cornea, 
and  consists  of  a  number  of  layers  (about  sixty)  of  white 
fibrous  tissue  arranged  parallel  to  one  another.  It  is  due  to 
this  arrangement  that  this  organ  is  transparent.  In  addi- 
tion to  these  fibres,  there  are  others  that  penetrate  the  organ 
at  a  right  angle  to  the  layers,  and  bind  all  together.  These 
are  the  perforating  fibres.  Between  the  various  layers  are 
a  large  number  of  irregular  spaces  called  the  corneal  la- 
cunae. These  contain  large  stellate  cells  that  are  the  origi- 
nal connective  tissue  cells  of  the  organ.  They  are  the  cor- 
neal CORPUSCLES.  The  spaces  communicate  with  one  an- 
other by  means  of  little  canals  called  canaliculi,  into  which 
their  processes  extend.  These  spaces  are  readily  shown 
by  the  gold  chlorid  method  of  staining. 

The    POSTERIOR    LIMITING     MEMBRANE,    Or    MEMBRANE    OF 

Descemet,  is  analagous  to  the  anterior  membrane;  unlike 


THE    CHOROII).  247 

this  one,  however,  it  is  thicker  peripherally  than  centrally; 
and  seems  more  independent  of  the  substantia  propria  than 
the  anterior.  It  docs  not  respond  to  the  clastica  stain,  and, 
consequently,  is  not  made  up  of  elastic  tissue,  as  its  name 
would  seem  to  indicate.     It  becomes  the  pectinate  ligament. 

The  ENDOTHELIAL  LAYER  cousists  of  a  single  layer  of  well- 
defined  regular  cells,  which  cover  the  posterior  surface  of 
this  organ,  and  continues  over  the  anterior  surface  of  the 
iris.  These  cells  are  hexagonal,  and  possess  a  fibrillar  pro- 
toplasm that  seems  to  extend  through  several  layers. 

The  cornea  possesses  blood-vessels  during  the  develop- 
mental period ;  these,  however,  disappear  before  birth,  so 
that  none  are  then  present.  Lymph,  which  circulates  through 
the  many  spaces  and  canaliculi,  nourishes  the  cornea. 

The  sclera  possesses  but  few  vessels,  and  these  are  found 
chiefly  at  the  corneo-scleral  junction,  where  a  circular  net- 
work is  formed. 

The  nerves  are  sensory;  at  the  corneo-scleral  junction,  a 
circular  plexus  is  formed,  from  which  fibres  pass  into  the 
substantia  propria,  while  others  penetrate  the  anterior  elastic 
lamina  to  pass  into  the  epithelial  layer.  Some  of  these  fibres 
extend  almost  to  the  surface. 

The  Middle  Coat,  or  tunic,  also  called  the  Uveal  Tract, 
is  the  vascular  coat.  It  contains  the  main  vessels  of  the 
eyeball,  except  the  central  artery  of  the  retina,  and  consists 
of  the  Choroid,  Ciliary  Body  and  Iris. 

The  Choroid  is  the  vascular  portion,  and  is  divided  into 
three  layers,  the  stroma  layer,  the  chorio-capillaris,  and 
the  glassy  membrane. 

The  stroma  layer  is  sometimes  referred  to  as  the  layer 
of  large  vessels,  as  they  are  found  only  in  this  portion.  It 
consists,  externally,  of  delicate  fibres  that  connect  with  those 
of  the  subscleral  tissue  and  form  a  complete  space  the  supra- 


248 


THE  EYEBALL   AND  LACRIMAL   SYSTEM. 


CHOROIDAL,    or    SUBSCLERAL    LYMPH     SPACE.        Ill    this    tisSUe 

are  found  pigmented  connective  tissue  cells,  and  it  has  re- 
ceived the  name  of  lamina  suprachroidea.  The  main  por- 
tion of  the  stroma  layer  consists  of  bundles  that  are  closely 
arranged.  The  network  formed  by  these  are  the  venous 
trunks,  externally,  and  the  arterial  trunks,  internally ;  the 
latter  are  accompanied  by  bundles  of  muscle  tissue.  Pig- 
mented cells  exist  between  the  bundles. 


«— ES 


Fig.  86. — CoRNEO- Scleral  Junction  of  Man. 
1.  Epithelium ;  2.  connective  tissue  of  conjunctiva ;  3.  sclera ;  4,  5,  6,  7 
and  8.  ciliary  body ;  4.  meridional  ;  5.  radial  ;  6.  circular  fibres  of 
ciliary  muscle ;  7.  ciliary  process ;  8.  pars  ciliaris  retinae ;  9.  pars 
iridica  retinae ;  10.  stroma  of  iris ;  11.  posterior  elastic  lamina  of 
cornea :  12.  substantia  propria :  13.  epithelium :  14.  canal  of 
Schlemm  ;  15.  angle  of  iris,  or  infiltration  angle   {Stohr's  Histology). 


The  inner  portion  of  this  layer  is  called  the  boundary 
zone;  the  bundles  are  arranged  into  several  layers  in  herb 
ivorous  animals,  so  as  to  give  a  peculiar  metallic  reflex,  and 
is  called  the  tapetum  fibrosum.  This  area  is  usually  free 
from  pigment  cells.  In  the  carnivorous  animals,  the  fibres 
are  replaced  by  distinct  cells  that  contain  crystals.  The 
metallic  reflex,  however,  is  the  same.  This  constitutes  the 
tapetum  cellulosum. 


CILIARY    BODY    AND    PROCESSES.  249 

The  CHORio-CAPiLLARis  coiitaiiis  little  stroma,  and  is  com- 
posed chiefly  of  a  dense  capillary  plexus.  No  pigment  cells 
are  seen.  The  capillaries  are  most  numerous  around  the 
macula  latea. 

The  GLASSY  MEMBRANE  lies  at  the  inner  boundary  of  the 
choroid,  and  consists  of  refractile  homogeneous  tissue.  It  is 
a  very  thick  basement  membrane,  and  supports  the  pig- 
mented cells  of  the  retina. 

The  choroid  extends  to  the  ora  serrata,  a  peculiar,  ser- 
rated line,  at  which  the  nervous  portion  of  the  retina  ceases. 
At  this  point,  the  choroid  continues  as  the  Ciliary  Body. 

The  Ciliary  Body  is  composed  of  three  main  portions, 
the  Ciliary  Ring,  the  Ciliary  Process  and  the  Ciliary 
Muscle.  It  is  thicker  than  the  choroid,  which  is  due  espe- 
cially to  the  addition  of  the  muscle  tissue. 

The  Ciliary  Ring  is  practically  the  continuation  of  the 
stroma  layer  of  the  choroid  and  the  boundary  membrane,  and 
consists  of  dense  white  fibrous  tissue,  which  forms  a  circular 
band  about  4  mm.  in  breadth.  The  vessels  have  a  longi- 
tudinal course. 

The  Ciliary  Processes  are  projections  of  the  stroma,  cov- 
ered by  pigmented  epithelial  cells,  from  60  to  80  in  number. 
They  arise  at  the  junction  with  the  choroid,  and  extend 
toward  the  iris,  increasing  in  height,  ending  abruptly  at 
that  point.  At  this  place,  they  are  about  i  mm.  in  height. 
Each  process  consists  of  a  core  of  stroma  (connective  tissue) 
supporting  blood-vessels  and  covered  by  the  pigmented  epi- 
thelial cells  of  the  retina,  the  pars  ciliaris  retinae.  These 
cells  rest  upon  a  continuation  of  the  glassy  membrane.  There 
are  two  layers,  the  outer  of  which  consists  of  low  columnar 
or  cuboidal  elements  that  are  the  continuation  of  the  true 
pigmented  cells  of  the  retina.  The  inner  layer  is  composed 
of  cells  that  are  columnar,  possess  little  or  no  pigment,  and 
are  the  representative  of  the  optical  portion  of  the  retina. 


250  THE  EYEBALL   AND   LACRIMAL   SYSTEM. 

The  Ciliary  Muscle  is  of  the  nonstriated  variety,  and  Hes 
external  to  the  ciHary  ring,  just  beneath  the  sclera.  The 
fibres  are  arranged  in  meridional,  radial  and  circular 
sets.  The  meridional  are  the  outermost,  and  extend  from 
the  canal  of  Schlemm,  in  the  corneo-scleral  junction,  to  the 
ciliary  ring.  These  are  the  tensor  muscles  of  the  choroid. 
The  radial  fibres,  which  compose  the  middle  layer,  extend 
peripherally,  and,  spreading  fan-like,  are  inserted  into  the 
ciliary  ring  and  processes.  The  circular  fibres  are  the 
inner  ones,  and  their  direction  is  equatorial.  They  consti- 
tute Muller's  ring-muscle. 

The  ciliary  region  is  indicated,  externally,  by  a  band  about 
one-fourth  of  an  inch  broad,  starting  at  the  corneo-scleral 
junction.  It  is  called  the  danger  zone  of  the  eyeball,  as  in- 
juries here  usually  result  fatally  to  sight. 

The  Iris  is  the  continuation  of  the  stroma  layer  and  glassy 
membrane  of  the  choroid.  It  receives,  also,  the  posterior 
lamina  and  the  endothelium  of  the  cornea,  and  consists  of 
the  anterior  endothelium,  stroma  layer,  posterior  lam- 
ina and  PIGMENT  layers. 

The  anterior  endothelium  is  a  continuation  of  that  of 
the  cornea,  and  covers  the  anterior  surface  of  the  iris.  The 
cells  are  neither  so  regular  nor  distinct  as  those  of  the  cornea. 

The  STROMA  LAYER  is  composcd  chiefly  of  a  coarse  net- 
work of  white  fibrous  tissue,  some  of  which  is  circularly  ar- 
ranged around  the  blood-vessels,  which  possess  no  muscular 
coat.  Anteriorly,  this  stroma  is  very  much  reticulated,  and 
forms  a  support  for  the  endothelial  cells.  According  to  some 
authors,  this  portion  constitutes  an  anterior  limiiing  mem- 
brane. In  the  stroma  layer,  pigment  cells  are  found  in  vary- 
ing quantities ;  in  gray  eyes,  very  few  are  seen ;  as  the  color 
passes  to  blue,  brown  and  black,  the  number  increases,  the 
last  possessing  the  most.     In  albino  eyes,  not  only  are  the 


THE    CORNEO-SCLERAL    JUNCTION.  25I 

pigmented  connective  cells  of  the  stroma  layer  absent,  but 
the  pigment  that  is  usually  present  in  the  posterior  epithelial 
cells  continued  from  the  retina,  is  also  absent.  As  a  result 
of  this,  the  retinal  blood-vessels  cause  a  peculiar  red  reflex, 
the  retinal  reflex.    In  the  other  eyes  the  pigment  obscures  it. 

In  the  stroma,  is  found  muscle  tissue  of  the  involuntary 
non-striated  variety.  This  is  arranged  circularly  and 
RADIALLY.  The  CIRCULAR  fibres  are  near  the  anterior  part  of 
the  iris,  and  contract  the  pupil,  when  stimulated ;  these  form 
the  SPHINCTER  pupillae  muscle.  The  radial  fibres  lie  near 
the  posterior  part,  and  when  they  contract,  the  pupil  is  di- 
lated ;  they  constitute  the  dilator  pupillae  muscle. 

The  posterior  limiting  membrane,  or  membrane  of 
Bruch,  is  a  continuation  of  the  glassy  membrane.  It  sup- 
ports the  pigmented  cells,  the  pars  iridica  retinae. 

The  pigmented  layer,  a  continuation  of  the  pars  ciliar- 
is  retinae,  and  called  the  pars  iridica  retinae,  is  usually 
pigmented,  and  consists  of  two  layers  of  cells.  It  continues 
to  the  anterior  margin  of  the  pupil. 

The  PUPIL  is  the  aperture  in  the  iris.  Its  size  is  regulated, 
autom.atically,  by  the  amount  of  light  entering. 

The  Corneo-scleral  junction  is  the  region  in  which 
cornea,  sclera,  ciliary  body  and  iris  come  together.  The 
sclera  passes  over  into  the  cornea,  but  the  line  of  transition 
is  not  abrupt,  but  gradual,  and  forms  an  oblique  line  that 
extends  from  before,  backward  and  inward.  Beneath  the 
posterior  margin,  usually  within  the  sclera,  is  a  circular 
canal,  the  canal  of  Schlemm,  which  extends  around  the 
corneo-scleral  junction.  In  this  region,  the  membrane  of 
Descemet  is  seen  to  divide  into  a  large  number  of  fibres 
that  extend  to  the  base  of  the  iris.  Between  the  fibres  are 
a  large  number  of  intercommunicating  spaces  called  the 
SPACES  OF  FoNTANA.     Thcsc  spaccs  lie  around  the  angle 


252 


THE   EYEBALL   AND  LACRIMAL   SYSTEM. 


formed  by  the  cornea  and  iris,  called  the  infiltration 
ANGLE,  and  communicate  with  the  anterior  chamber  and  thi: 
canal  of  Schlemm.  The  network  is  called  the  pectinate 
LIGAMENT,  and  is  lined  by  endothelial  cells. 

THE  RETINA. 
The  Retina  forms  the  internal,  or  nervous,  coat  of  the 
eyeball.  It  may  be  divided  into  two  portions,  the  pars 
OPTICA,  that  portion  capable  of  vision,  and  the  pars  ceca,  or 
the  blind  part,  possessing  no  nervous  elements.  The  latter 
portion  is  further  subdivided  into  pars  ciliaris  and  pars 


Fig.  87. — Vertical  Section  op  Retina  op  a  Rabbit  {Stdhr's  Histology). 

1.  Pigment  layer ;  2.  rods  and  cones ;  3.  external  limiting  membrane ; 
4.  outer  granule  layer ;  5.  outer  reticular  layer ;  6.  inner  granule 
layer  ;  7.  inner  reticular  layer ;  8.  ganglion-cell  layer  ;  9.  nerve  fibre 
layer ;  10.  inner  limiting  membrane ;  a.  expanded  base  of  a  Mtiller 
fibre  ;  h.  nucleated  portion  of  same. 

IRIDICA  RETINAE.  The  simplest  division  of  the  retina,  how- 
ever, is  PARS  OPTICA,  PARS  CILIARIS  and  pars  IRIDICA 
RETINAE. 

The  PARS  OPTICA  lines  almost  the  entire  optic  cup,  and  ex  • 
tends  forw^ard  to  the  end  of  the  choroid.  Here  the  nervous 
portion  ceases,  and  the  coat  becomes  abruptly  thinner,  and 
forms  an  irregular  serrated  line,  the  ora  serrata.  From 
this  point,  the  last  two  portions  of  the  retina  continue. 


THE   RETINA.  253 

The  Optical  portion  consists  of  eleven  layers,  counting  the 
pigmented  layer.     These  layers  are  classed  as  neuro-epi- 

THELIAL     and     CEREBRAL.        The     NEURO-EPITHELIAL     pOrtion 

consists  of  the  first  five  layers  within  the  pigment  layer,  and 
the  CEREBRAL  portion  the  remaining  divisions.  The  pig- 
mented part  is  derived  from  the  outer  layer  of  the  optic  cup, 
and  the  the  other  parts  from  the  inner  layer. 

Optic  Vesicle.  Retinal  Layer.         Classes. 

Outer  Layer.  Pigmented  Layer PIGMENT  LAYER. 

/Layer  of  rods  and  cones. 

j  External  limiting  membrane  NEURO-EPITHELIAL 
I  Outer  granular  layer.  LAYER. 

]  Henle's  fibre  layer. 

T  T  /  Outer  RETICULAR  (molecular) 

Inner  Layer  \  \  ' 

] Outer  ganglionic   (inner  granule). 

/Inner  reticular  (molecular). CEREBRAL. 

I  Inner  ganglionic. 

\  Nerve  fibres. 

^Internal  limiting  membrane. 

The  PIGMENT  LAYER  consists  of  polyhedral  cells  contain- 
ing a  black,  granular,  mobile  pigment.  The  position  occu- 
pied by  this  pigment  depends  upon  the  presence  or  absence 
of  the  light.  The  nonpigmented  nuclei  occupy  the  basal  por- 
tion of  the  cell.  These  cells  continue  over  the  ciliary  body 
and  iris  as  the  pars  ciliaris  and  iridica  retinae.  In  the 
iris,  both  layers  are  pigmented,  but  not  in  the  ciliary  region. 
This  layer  is  derived  from  the  outer  layer  of  the  optic  cup. 

The  nervous  structures  are  supported  by  neuroglia,  of 
which  a  great  deal  is  present,  and  unevenly  distributed. 

The  LAYER  OF  RODS  AND  CONES  is  the  most  important  por- 
tion of  the  retina. 

The  CONES  consist  of  cell-body  and  cone-fibre.  The 
(iELL-BODY  is  about  30  microns  in  length,  and  is  divided  into 


254  THE   EYEBALL   AND  LACRIMAL   SYSTEM. 

two  segments,  cuter  and  inner.  The  outer  is  conical,  may 
be  striated,  rests  upon  the  Hmiting  membrane,  and  is  ap- 
parently composed  of  discs.  The  inner  segment  is  striated 
and  flask-shaped.  At  its  junction  with  the  outer  segment, 
it  is  granular,  and  the  other  part  is  fibrillar.  The  cone-fibre 
ends  in  the  outer  reticular  layer,  and  has  a  nucleus  near  its 
junction  with  the  body. 

The  RODS  are  longer  than  the  cones,  averaging  about  50 
microns.  They  have,  somewhat,  the  same  structure  as  the 
preceding  and  are  alm.ost  uniform  in  size.  The  different  seg- 
ments react  differently  to  stains.  The  outer  segment  pos- 
sesses prominent  cross  and  faint  longitudinal  striations.  In 
this  portion  of  the  cell,  the  rhodopsin,  or  visual  purple, 
is  located.  The  ij'iner  segment  is  spindle-shaped,  granu- 
lar, and  fibrillar  like  the  above.  The  rod-Hhres  terminate 
in  the  outer  reticular  layer,  where  they  are  enlarged.  The 
nuclei  lie  in  the  outer  granular  layer.  They  may  be  ir- 
regularly placed,  and  in  lower  animals,  may  even  be  striated. 

Usually,  three  or  four  rods  are  seen  to  each  cone.  In 
the  central  portion  of  the  yellow  spot,  the  cones  alone  are 
present. 

The  EXTERNAL  LIMITING  MEMBRANE  COUsistS  of  the  OUtcr 

ends  of  the  fibres  of  Miiller.  These  run  radia-lly,  and  ex- 
tend through  almost  the  entire  thickness  of  the  retina.  The 
outer  ends  of  these  fibres  are  enlarged,  and  lie  so  close  to- 
gether that  they  form  a  membrane,  the  outer  limiting 
MEMBRANE.  Thcsc  fibres  do  not  penetrate  the  rod  and  cone 
layer,  but  give  branches  to  all  of  the  other  layers.  Each 
fibre  possesses  a  nucleus  that  lies  in  the  inner  nuclear  layer. 
At  their  internal  ends,  they  are  again  enlarged,  and  form 
the  INTERNAL  LIMITING  MEMBRANE.  GHa  cclls  are  also 
present. 

The  OUTER  GRANULE,  or  NUCLEAR  LAYER  consists  of  sev- 
eral layers  of  oval  nuclei,  which  are  the  granules.    These  are 


TPIE    RETINA.  255 

the  nuclei  of  the  rod  and  cone-fibres.  The  former  are  the 
more  numerous. 

Henle's  fibre  layer  is  best  developed  in  the  macular 
region,  from  which  area  it  diminishes  peripherally.  It  is 
made  up  of  the  inner  segments  of  the  rod  and  cone-fibres. 

The  OUTER   MOLECULAR,  Or  RETICULAR  LAYER  is   COmpOScd 

of  the  inner  ends  of  the  rod  and  cone  cells,  which  are 
branched,  and  fibrillar,  and  proceed  from  the  inner  nuclear 
layer. 


A 


y^ 


Y 


Fig.  88. — Cells  from  Retina  of  an  Ape  (Stohr's  Histology). 
1.  Cell  of  ganglion  of  optic  nerve.  2.  Cells  of  inner  granule  layer.  3.  Rod- 
cells  :  a.  outer  segment ;  b.  inner  segment :  A:,  rod-granule ;  x.  fibre- 
apparatus.  Below  are  rod-cells  and  fragments,  4.  Cone-visual  cells ; 
a.  outer  segment;  i.  inner  segment:  k.  cone-granule;  f.  cone-fibre; 
X.  fibre  apparatus.  5.  Radial  fibre,  Miiller's  fibre  :  k.  nucleus ;  r.  pyra- 
midal base. 

The    INNER    GRANULAR,    or    OUTER    GANGLIONIC/  LAYER    is 

made  up  of  several  varieties  of  closely  packed  cells,  the  most 
numerous  of  which  are  oval,  bipolar  elements.  These 
are  placed  vertically,  and  the  smiall  amount  of  protoplasm 
present  continues  as  an  inner  process  that  passes  to  the  inner 
molecular  layer ;  here  it  breaks  into  many  branches  that  form 
a  network  around  the  ganglion  cells.  The  outer  process  of 
these  oval  cells  surround  the  ends  of  the  rod-fibres  in  the 
form  of  a  delicate  rete,  or  mesh  of  fibrillae.  Other  cell- 
processes  pass  to  the  cone-fibres  and  to  the  inner  molecular 
layer. 


256  THE   EYEBALL   AND  LACRIMAL   SYSTEM. 

Another  kind  of  cell  is  present,  the  amakrine  cell, 
which  forms  a  layer  near  the  inner  boundary  of  this 
nuclear  layer.  These  cells  possess  no  axis-cylinders,  but 
other  processes  extend  into  the  inner  molecular  layer. 

A  third  variety  possesses  a  cell-body,  the  long  diameter 
of  which  lies  parallel  to  the  surface  of  the  retina.  The  pro- 
cesses pass  into  the  outer  molecular  layer.  Some  connect 
with  the  rod-fibres ;  these  are  larger,  and  lie  internally,  while 
the  others  that  pass  to  the  cone-fibres  are  smialler,  and  have 
an  external  position. 

In  addition  to  the  above,  there  are  some  cells  present  in 
this  layer  that  send  their  axis  cylinders  into  the  optic  nerve. 

The  nuclei  of  Miiller's  fibres  lie  in  this  layer. 

The    INNER   RETICULAR,    Or   MOLECULAR,   LAYER    COUsistS    of 

fibrils  of  cells  of  the  preceding  layer  and  from  cells  of  the 
inner  ganglionic  layers.  The  fibres  lie  at  dififerent  levels, 
which  gives  them  a  striated  appearance. 

The  GANGLIONIC  (inner)  layer  is  composed  of  a  single 
layer  of  multipolar  ganglion  cells.  The  cell-bodies  are  flask- 
shaped,  .and  the  axis  cylinders  pass  into  the  layers  of  nerve 
fibres.  The  dendritic  processes  extend  into  the  inner  mole- 
cular layer  at  different  levels,  and,  supposedly,  do  not  com- 
municate with  those  of  other  cells.  In  the  region  of  the 
macula  lutea,  these  cells  become  increased  in  number,  form- 
ing, often,  eight  layers. 

The  LAYER  OF  nerve  fibres  is  the  expanded  optic  nerve. 
These  fibres  pierce  all  the  layers,  except  the  internal  limit- 
ing membrane.  They  enter  the  eyeball  through  the  cribri- 
form LAMINA  of  the  sclera,  ^t  which  point  the  medullary 
sheaths  are  lost,  and  when  the  layer  of  nerve  fibres  is 
reached,  these  nonmedullated  fibres  diverge.  As  most  of 
the  fibres  pass  from  the  ganglion  cells  toward  the  brain,  it 
would  be  better  to  say  that  they  converge  at  the  optic  nerve 


THE    OPTIC    NERVE.  257 

entrance,  where  the  layer  of  nerve  fiijres  is  thickest,  and 
decreases  as  the  ora  serrata  is  approached. 

The  INTERNAL  LIMITING  MEMBRANE  is  formed  by  the 
fusion  of  the  inner  ends  of  Miiller's  fibres. 

There  are  three  important  areas  in  the  retina,  i.  the  optic 

NERVE  ENTRANCE,  OPTIC  PAPILLA,  or  BLIND  SPOT,  2,  the  MA- 
CULA LUTEA,  or  YELLOW  SPOT,  and,  3,  the  ora  serrata. 

1.  In  the  BLIND  spot,  only  the  layer  of  nerve  fibres  is  pres- 
ent. It  lies  about  one-eighth  of  an  inch  to  the  nasal  side,  and 
about  one-tenth  of  an  inch  below  the  optic  axis.  In  the 
center  is  usually  -a  shallow  depression ;  around  the  edge,  it 
is  raised,  and  forms  the  papilla  nervi  optica. 

2.  The  YELLOW  SPOT  is  in  the  direct  visual  axis.  The  color 
is  due  to  the  presence  of  a  diffuse  yellow  pigment.  Its  edge 
is  raised,  owing  to  the  great  thickness  of  the  inner  ganglion- 
ic layer.  From  the  edge  to  the  center,  all  the  layers  de- 
crease and  disappear,  so  that  in  the  center,  the  fovea  cen- 
tralis, the  cones  alone  are  pt^es^nt.  H^re  vision  is  most 
acnte. 

3.  At  the  ORA  SERRATA,  all  of  the  nervous  layers  end  ab- 
ruptly, and  are  continued  as  a  single  layer  of  cuboidal  or 
columnar  cells.     Beyond  this  point,  there  is  no  vision. 

The  light  rays  falling  upon  the  retina  are  not  transmitted 
to  the  brain  by  a  direct  route.  The  impressions  are  received 
by  the  rods  and  cones,  which  send  impulses  to  the  cells  of 
the  outer  reticular  layer;  these  cells  communicate  with  the 
ganglion  cells,  and  the  impulses  are  carried  to  the  brain  by 
the  axis-cylinders  of  these  cells,  as  they  form  the  optic  nerve. 

The  Optic  Nerve  consists  of  a  single  bundle  of  nerve 
fibres  that  possess  no  neurilemma.  It  is  surrounded  by  the 
dura,  arachnoid,  and  pia,  continued  from  the  brain.  The 
lymph  spaces  included  within  these,  communicate  with  those 
of  the  eyeball.     The  dura  and  pia  pass  over  into  the  sclera. 


258  THE  EYEBALL   AND  LACRIMAL   SYSTEM. 

but  the  arachnoid,  as  such,  is  lost  before  this  occurs ;  as  a 
result,  the  two  lymph  spaces  between  these  three  layers  be- 
come one.  The  nerve  fibres  penetrate  the  sclera  through  the 
LAMINA  CRiBROSA.  As  they  pass  through  this  coat,  they  lose 
the  medullary  sheath,  so  that  they  become  nonmedullated 
fibres  when  they  enter  the  retina. 

VITREOUS  BODY  AND  LENS. 

Of  the  REFRACTIVE  MEDIA  of  the  eyeball,  the  Vitreous  and 
Aqueous  Humors  and  the  Lens  are  yet  to  be  described. 

The  Vitreous  Humor,  or  Body,  occupies  the  optic  cup, 
or  VITREOUS  CHAMBER.  This  body  consists  of  a  fine  limiting 
membrane,  the  hyaloid  membrane,  a  delicate  homogene- 
ous structure  enclosing  the  substance  of  the  organ,  which 
is  composed  of  about  98  per  cent  water  and  2  per  cent,  solid 
elements.  The  latter  comprise  connective  tissues  and  wan- 
dering cell,  and  some  fibrils. 

This  organ  is  traversed  by  a  small  canal,  called  the  canal 
OF  Stilling,  or  hyaloid  canal.  This  extends  from  the 
optic  nerve  to  the  lens,  and  in  intra-uterine  life  is  occupied 
by  a  branch  of  the  retinal  artery,  the  hyaloid  artery,  that 
passes  to  the  lens. 

The  Aqueous  Humor  is  practically  lymph.  It  occupies 
the  anterior  and  posterior  chambers,  and  as  a  refractive 
medium,  is  unimportant. 

The  Crystalline  Lens  is  a  solid  body,  and  the  most  im- 
portant refractive  medium  of  the  eyeball.  It  possesses  two 
curvatures,  of  which  the  anterior  is  the  greater.  It  lies  in  a 
depression  of  the  vitreous  humor,  called  the  patellar  fossa, 
and  is  held  in  position  by  the  suspensory  ligaments. 

The  LENS  consists  of  a  capsule,  within  which  lies  the  Jens 
substance.  The  capsule  is  composed  of  delicate  white  fibrous 
tissue,  and  to  it  are  attached  the  ligaments.  This  is  thicker 
anteriorly,  and  seems  composed  of  layers. 


THE   CHAMBERS   OF  THE  EYEBALL.  259 

The  SUBSTANCE  OF  THE  LENS  is  of  epithelial  origin,  and 
consists  of  LENS  FIBRES  that  are  greatly  elongated  cells. 
Upon  the  anterior  surface,  just  beneath  the  capsule,  is  a 
single  layer  of  cuboidal  cells  called  the  lens  epithelium. 
At  the  equator  of  the  lens,  these  cells  lengthen,  forming  the 
LENS  FIBRES,  which  are  hexagonal,  nucleated  structures. 
The  nuclei  are  large  and  oval,  and  lie  near  the  middle  of  the 
fibres.  Peripherally,  the  fibres  are  harder  than  those  of  the 
center. 

The  Suspensory  Ligament  of  the  lens  is  really  a  con- 
tinuation of  the  hyaloid  membrane,  and  is  composed  of  a 
large  number  of  fibres  that  pass  from,  the  anterior  and  poster- 
ior layers  of  the  capsule.  Those  from  the  anterior  layer  pass 
into  the  depressions  between  the  ciliary  processes,  while 
those  from'  the  posterior  layer  are  attached  to  the  summits 
of  the  proce^sses.  Between  these  two  layers  of  fibres  is  a 
small  space,  the  canal  of  Petit.  This  region  constitutes  the 

ZONE   OF  ZiNN. 

The  Chambers  of  the  eyeball  are  Anterior,  Posterior 
and  Vitreous.  The  Anterior  lies  between  the  iris  and 
cornea  the  Posterior  between  the  lens  and  vitreous  humor, 
and  the  Vitreous  is  occupied  by  the  vitreous  body.  These 
are  large  lymph  spaces,  and  are  connected  with  one  another, 
and  with  the  other  spaces  of  the  eyeball. 

The  circulation  of  the  eyeball  is  carried  on  by  the  central 

ARTERY  OF  THE  RETINA,  the  LONG  and  SHORT  POSTERIOR  and 
the  ANTERIOR  CILIARY  ARTERIES. 

The  RETINAL  ARTERY  passcs  into  the  eyeball  through  the 
center  of  the  optic  nerve,  and  forms  a  zi^horl  of  branches 
upon  its  entrance.  These  vessels  extend  to  the  ora  serrata. 
The  layer  of  rods  and  cones  and  the  macula  lutea  possess 
no  blood-vessels.  The  blood  is  collected  by  venous  stems, 
which  form  the  central  vein  of  the  retina  that  has  a  course 
parallel  to  the  artery. 


26o 

Cornea. 


THE  EYEBALL   AND  LACRIMAL   SYSTEM. 


^: 'i^'J'l^JX-^j^ 


^  Anterior  ciliary  artery. 

^^  Anterior  ciliary  vein. 

o  connection      with      circulus 

'         major. 

y  Connection  with  chorio-capillaris. 
d  Arterial  episcleral  branches. 
8'  Venous  episcleral  branches. 

^  Arterial  conjunctival  branches. 

£  Venous  conjunctival  branches. 

^  Arterial  branches  to  corneal  junction. 

^y  Venous  branches  to  corneal  junction. 

V  Venae  vorticosae. 

S  Venous  sinus  of  sclera. 


Fig.  89. — ^Vessels  of  the  Eye.     External  tunic,  stippled ;  middle  tunic, 

white ;   internal   tunic  and  optic  nerve,   stippled   criss-cross ; 

arteries,   light ;   veins,   dark. 

Central  vessels  of  retina :  a.  artery  ;  a',  vein  ;  b,  c,  d.  anastomoses  wth 
vessels  of  sheath,  short  posterior  ciliary  arteries  and  choroidal  ves- 
sels, respectively. 

A,  Inner,  B,  outer  sheath  vessels ;  i.  short  posterior  ciliary  artery ;  i'.  vein  ; 
II.  episcleral  artery ;  II'.  veins ;  III.  capillaries  of  chorio-capillaris. 
1.  long  posterior  ciliary  artery  :  2.  circulus  iridicus  major ;  3.  branches 
to  ciliary  body;  4.  to  iris  {StOhr's  Histology), 


THE   CIRCULATION   OF  THE   EYEBALL.  261 

The  SHORT  POSTERIOR  CILIARY  arteries  are  about  twenty  in 
number.  They  pierce  the  sclera  near  the  entrance  of  the 
optic  nerve,  and  pass  into  the  choroid.  As  they  pass  through 
the  sclera,  they  give  off  branches  that  supply  the  posterior 
half  of  this  coat.  In  the  choroid,  these  vessels  form  the 
chorio-capillaris.  Their  branches  anastomose  with  branches 
of  all  others,  including  those  of  the  central  artery  of  the 
retina. 

The  LONG  POSTERIOR  CILIARY  arteries  pierce  the  sclera 
near  the  optic  nerve,  and  pass  to  the  ciliary  region  between 
the  choroid  and  sclera.  At  the  base  of  the  iris,  they  form 
a  circle  of  vessels,  the  circulus  arteriosus  iridicus 
MAjOR^,  which  sends  branches  to  the  ciliary  processes,  the 
choroid  and  the  iris ;  the  latter  branches  pass  to  the  pupillary 
region,  where  they  form  the  circulus  iridicus  minor. 

The  ANTERIOR  ciliary  arteries  are  derived  from  the  ves- 
sels of  the  recti  muscles.  These  penetrate  the  sclera  near 
the  corneo-scleral  junction.  Their  branches  nourish  the  an- 
terior half  of  the  sclera,  the  conjunctiva,  the  ciliary  muscle, 
and  the  anterior  half  of  the  choroid;  they  connect  with  the 
circulus  iridicus  major,  and  form  a  network  of  capillaries 
at  the  corneo-scleral  junction.  Around  the  optic  nerve,  there 
is  some  anastomosis  between  the  branches  of  the  ciliary 
arteries. 

The  blood  is  returned  by  the  venae  vorticosae,  which  are 
four  to  six  in  number.  These  run  a  course  entirely  different 
from  that  of  the  arteries.  Each  is  formed  by  a  whorl  of 
veins,  and  passes  through  the  sclera  to  empty  into  the  oph  • 
thalmic  veins.  The  blood  from  the  anterior  ciliary  arteries 
is  carried  by  the  anterior  ciliary  veins  that  run  parallel  to  the 
arteries.  These  also  receive  the  blood  from  the  episcleral 
spaces. 

The  lymphatics  are  extensive,  and  form  a  series  of  inter- 
communicating spaces. 


262  THE  EYEBALL  AND  LACRIMAL   SYSTEM. 

Anteriorly,  the  spaces  in  the  cornea  communicate  with 
those  of  the  sclera,  and  with  the  canal  of  Schlemm  and  the 
anterior  chamber,  by  means  of  the  spaces  of  Fontana. 

The  ANTERIOR  CHAMBER  communicatcs  with  the  posterior 
chamber,  and  through  this,  with  the  canal  of  Petit. 

Posteriorly,  the  lymphatics  of  the  optic  nerve  communi- 
cate with  the  subarachnoidean  space,  on  the  one  hand,  and 
the  hyaloid  canal  and  perivascular  spaces  of  the  retina,  on 
the  other. 

The  space  of  Tenon  lies  external  to  the  sclera,  and  re- 
ceives lymph  from  the  subscleral  space,  directly,  and  by 
way  of  the  channels  around  the  venae  vorticosae;  the  lymph 
is  sent  to  the  spaces  around  the  optic  nerve.  The  latter 
communicate  with  those  of  the  central  nervous  system. 

The  nerves,  long  and  short  ciliary,  supply  the  choroid 
and  pass  between  it  and  the  sclera;  at  the  ciliary  body, 
they  form  the  ciliary  ganglion  plexus,  that  supplies  the 
ciliary  muscle,  iris  and  cornea  and  vessels.  Those  of  the  iris 
form  a  circular  plexus.  The  nerves  of  the  cornea  have  been 
considered. 

THE  APPENDAGES  OF  THE  EYEBALL. 

The  Appendages  are  the  Eyelids,  Conjunctiva  and  the 
Caruncle. 

The  Eyelid  consists  of  a  double  fold  of  skin,  the  under 
surface  of  which  has  become  modified  to  form  a  mucous 
MEMBRANE.  This  is  the  conjunctiva,  which  is  composed 
of  stratified  columnar  cells  that  rest  upon  a  basement  mem- 
brane and  tunica  propria.  Among  the  epithelial  cells,  some 
goblet  cells  are  seen.  Over  its  greater  extent,  the  conjunc- 
tiva is  smooth,  but  toward  the  region  opposite  to  the  free 
edge,  folds  are  formed. 

Beneath  the  tunica  propria,  is  found  a  dense  plate  of  white 
fibrous  tissue  called  the  tarsal  plate  (incorrectly  called 


THE   EYELID. 


263 


cartilage).     This  is  wedge-shaped,  with  its  thicker  edge  at 
the  marg-in  of  the  Hd.     It  extends  a  Httle  over  one-half  the 


Fig.  90. — Sagittal  Section  of  Eyelid  of  a  Child  Six  Months 
Old  {Stohr^s  Histology). 
1.  Skin :  E.  epidermis ;  C.  derma ;  8c.  subcutaneous  tissue ;  Hb.  lanugo 
hairs ;  K.  sweat-glands ;  W.  eyelash  ;  Eh.  developing  lash  ;  W,  W". 
portions  of  follicle  of  eyelashes  ;  M.  portion  of  a  ciliary  gland.  2.  Or- 
bicularis palpebrarum  muscle ;  O.  transverse  section  of  same ;  McR. 
tarsal     muscle.  3.     Tendon     of     levator     palpebrarum     superior ; 

mps.  superior  levator  muscle.  4.  Conjunctival  portion;  e.  epithelium; 
tp.  tunica  propria ;  at.  accessory  tear  gland ;  *.  tarsus ;  m.  tarsal 
gland   (Meibomian)  ;  a.  arcus  tarseus  externus ;   5.  margin  of  eyelid. 

height  of  the  lid,  and  at  its  end,  an  accessory  tear  gland  is 
found,  the  gland  of  Krause.     It  contains  a  number  of 


264  THE  EYEBALL   AND  LACRIMAL   SYSTEM. 

compound  racemose  glands y  the  ducts  of  which  open  upon 
the  free  margin.  These  are  the  Meiboml\n,  or  tarsal, 
GLANDS,  and  number  about  thirty  in  the  upper,  and  a  few 
less  in  the  lower,  lid.  They  resemble  sebaceous  glands,  and 
the  ducts  are  lined  by  stratified  squamous  cells.  At  the 
margin  of  the  lid,  mmscle  fibres  .are  seen  to  surround  the 
ducts.  These  glands  secrete  an  oily  substance  that  lubricates 
the  edges  of  the  lids,  prevents  them  from  uniting,  and  ordi- 
narily keeps  the  tears  from  overflowing. 

Between  the  tarsal  plate  and  the  upper  skin  surface,  is 
found  the  subcutaneous  fibrous  tissue.  In  this  layer  is 
the  muscle  of  the  eyelid,  which  is  chiefly  of  the  voluntary 
variety,  although  some  smooth  muscle  is  present.  Some 
voluntary  muscle  fibres  are  found  between  the  cilia  and 
Meibomian  gland ;  these  constitute  the  marginal  muscle.  In 
the  tarsal  connective  tissue  are  found  smooth  muscle  fibres 
constituting  the  lid-muscle  of  Mueller. 

The  SKIN  covers  the  outer  surface.  Its  structure  is  the 
same  as  in  other  places,  and  it  contains  many  sebaceous  and 
sweat-glands  and  fine  hairs.  Pigmented  cells  are  found  in 
the  corium.  Very  little  fat  is  found  in  the  loose  subcutan- 
eous tissue. 

At  the  edge  of  the  lid,  are  seen  two  rows  of  heavy  hairs, 
the  CILIA,  or  eyelashes.  They  pass  deeply  into  the  corium, 
and  last  about  four  months.  Between  the  cilia  and  the  ducts 
of  the  Meibomian  glands,  are  some  coiled  tubular  structures 
called  the  glands  of  Moll.  These  are  ceruminous  glands, 
and  resemble  those  of  the  external  ear.  Their  ducts,  at 
times,  are  seen  to  open  into  the  follicles  of  the  cilia. 

The  skin  at  the  conjunctival  margin  forms  an  acute  angle, 
while  above  the  ciliary  region,  the  angle  is  obtuse.  This 
serves  to  distinguish  these  two  margins. 

The  Conjunctiva  lines  the  under  surface  of  the  eyelid,  and 
is  then  reflected  over  the  eyeball  from  the  insertion  of  the 


THE  LACRIMAL  APPARATUS.  265 

muscles  to  the  cornea.  Here  the  stratified  cells  alone  con- 
tinue upon  this  organ.  It  consists  of  stratified  columnar 
cells,  basement  membrane  and  tunica  propria.  In  the  latter, 
lymphoid  tissue  is  often  present  in  abundance. 

At  the  inner  angle,  or  canthus^  of  the  lids  is  seen,  in 
lower  animals,  a  third  eyelid.     This  is  called  the  plica 

SEMILUNARIS,   Or   MEMBRANA   NICTITANS.      In  lowcr  foHTlS,  a 

distinct  tarsal  plate  is  present,  which  is  seldom  present  in 
man.  Here  it  is  usually  a  small  fold,  covered  by  stratified 
squamous  cells,  in  which  some  glands  may  be  found. 

The  Caruncle  is  a  little  patch  of  skin  at  the  inner  canthus. 
It  contains  hair  follicles,  sweat-glands,  adipose  and  muscular 
tissues  within  its  corium,  and  is  covered  by  stratified  squam- 
ous cells.  A  little  voluntary  striated  and  some  smooth 
muscle  tissue  are  present. 

Within  the  eyelid,  tmo  arterial  arches  are  formed,  one 
at  the  upper  edge  of  the  tarsus,  the  external,  and  the  other 
at  the  edge  of  the  lid,  the  internal.  These  arches  are  pro- 
duced by  the  vessels  coming  from  the  inner  and  outer  canthi. 
The  smaller  branches  pass  to  the  glands  and  conjunctiva  of 
the  lid,  where  they  form  delicate  plexuses. 

The  lymphatics  form  a  close,  delicate  plexus  beneath  the 
conjunctiva,  and  a  loose  set  at  the  upper  margin  of  the  lid, 
that  communicate  with  each  other.  The  branches  of  the  lat- 
ter possess  valves. 

The  nerves  give  off  branches  to  the  muscles  and  skin,  and 
then  form  a  plexus  beneath  the  conjunctiva.  The  latter 
supplies  the  glands,  cilia  and  conjuncti'va,  forming,  in  the 
latter,  a  subepithelial  plexus  .and  special  endings,  such  as 

CONJUNCTIVAL    CORPUSCLES   and    END-BULBS. 

THE  LACRIMAL  APPARATUS. 

The  Lacrimal  Apparatus  consists  of  the  Lacrimal 
Gland,  the  Canaliculi,  the  Lacrimal  Sac  and  the  Naso- 
lacrimal  Duct. 


266  THE   EYEBALL    AND    LACRIMAL    SYSTEM. 

The  Lacrimal  Gland  is  a  compound  tubular  organ  of  a 
serous  character. .  Like  the  mammary  gland,  it  is  a  com- 
pjDund  gland,  as  it  is  composed  of  six  or  seven  individual 
glands  merely  bound  into  one  mass.  Each  has  its  own  duct 
that  opens  upon  the  conjunctival  surface. 

Each  Gland  is  covered  by  a  delicate  capsule  of  white 
fibrous  tissue  that  divides  it  into  lobes  and  lobules.  The 
LOBULES  consist  of  the  tubular  acini,  which  are  lined  by 
simple  cuhoidal  cells.  The  protoplasm  of  these  is  granular, 
and  the  nuclei  have  a  basal  position.  These  cells  rest  upon  a 
basement  membrane,  which  is  suported  by  interstitial  con- 
nective tissue  of  a  fibro-elastic  nature.  The  ducts  are  lined 
by  simple  columnar  cells. 

The  blood-vessels  are  numerous,  and  form  close  capillary 
plexuses  around  the  tubular  acini. 

The  nerves  form  a  subepithelial  plexus,  but  the  exact 
mode  of  ending  is  not  known. 

Each  Canaliculus  has  a  lining  of  stratified  squamous  cells 
that  rest  upon  the  tunica  propria  and  fibro-elastic  layer.  Out- 
side of  the  tunica  propria  is  seen  some  voluntary  striated 
muscle,  chiefly  longitudinally  arranged. 

The  opening  of  the  canaliculus  is  called  the  puncta,  and  at 
this  point,  some  of  the  muscle  fibres  are  circularly  disposed, 
forming  sphincter  muscles. 

The  Sac  and  Duct  are  lined  by  stratified  columnar  cells. 
In  the  tunica  propria,  considerable  diffuse  adenoid  tissue  is 
found.  Occasionally,  in  the  lower  end  of  the  duct,  cilia\ted 
epithelial  cells  are  present. 

Within  the  orbit,  the  eyeball  is  surrounded  by  a  serous 
membrane  called  the  capsule  of  Tenon.  The  space  enclosed 
is  the  space  of  Tenon,  or  the  episcleral  lymph  space.  This 
space  aids  in  the  movement  of  the  eyeball. 


CHAPTER  XIX. 


THE  EAR. 

The  Ear  is  made  up  of  three  parts,  the  External,  Middle 
and  Internal. 

The  EXTERNAL  EAR  receives  the  sound  waves  and  conducts 
them  to  the  middle  ear.  The  vibrations  of  the  drum  are 
carried  across  the  middle  ear  and  conducted  into  the  in- 
ternal EAR,  where  they  are  translated  into  the  proper  im- 
pressions. 

The  External  Ear  consists  of  the  Pinna  and  a  short 
Canal,  the  External  Auditory  Canal. 

The  Pinna  is  covered,  upon  both  sides,  by  skin,  and,  in 
its  center,  possesses  a  mass  of  elastic  cartilage.  It  is  very 
irregular,  but  adapted  to  catch  sound  waves.  The  skin 
possesses  hair  follicles  and  sebaceous  glands.  The  lobe, 
the  lower  soft  portion,  contains  no  cartilage,  and  is  very  vas- 
cular. 

The  External  Auditory  Canal  consists  of  outer,  car- 
tilaginous and  inner,  bony  portions.  The  outer  part  is 
lined  by  skin,  in  the  corium  of  which  are  found  cerumin- 
ous  GLANDS.  Thcsc  are  coiled  tubular  organs  that  form  the 
wax.  Hairs  are  very  abundant  here.  In  the  inner,  or 
osseous,  portion,  hairs  and  glands  are  absent,  and  the  tunica 
propria  is  closely  attached  to  the  periosteum  of  the  bone. 

The  Tympanic  Membrane,  or  Drum,  separates  the 
middle  from  the  external  ear.  Externally,  it  is  covered  by 
stratified  squamous  cells  continued  from  the  skin.  In  this 
location,  the  stratum  corneum  is  nucleated,  and  the  corium 
is  thin,  except  in  the  region  of  the  handle  of  the  malleus. 
The  middle  portion  consists  of  white  fibrous  tissues  arranged 
as  radial,  or  external,  and  circular,  or  internal  fibres. 

267 


268  THE    EAR. 

The  former  becomes  thinner  toward  the  center  of  the 
tympanum  and  disappears  entirely.  The  circular  fibres 
are  more  numerous  externally,  and  become  thinner  toward 
the  handle  of  the  malleus,  where  they  disappear.  Between 
these  two  layers,  is  a  small  amount  of  loose  connective  tis- 
sue. Peripherally,  the  fibrous  layer  becomes  thickened  to 
form  the  annulus  fibrosus.  The  internal  surface  is  cov- 
ered by  simple  squamioiis,  or  columnar,  cells  that  rest  upon 
a  basement  membrane.  In  the  flaccid  area  of  the  drum,  the 
middle  layer  is  absent,  so  that  the  internal  and  external  lay- 
ers touch  each  other. 

The  Middle  Ear,  or  Tympanum,  is  an  irregular  cavity 
within  the  bone,  and  is  connected  with  the  pharynx  by  the 
Eustachian  Tube.  This  maintains  an  equal  pressure  upon 
both  sides  of  the  membrane.  The  mucous  membrane  lining 
these  portions  is  covered  by  pseudo  stratified  ciliated  epi- 
thelium. The  cilia  are  absent  upon  the  ear  bones,  liga- 
ments and  MEMBRANA  TYMPANi.  Small  mucous  glands 
are  found  in  the  tunica  propria.  The  antrum  and  mastoid 
CELLS  are  lined  by  low  polygonal  cells. 

The  Ear  Bones  are  the  malleus,  incus  and  stapes. 
These  are  small  masses  of  osseous  tissue,  by  means  of  which 
the  sound  waves  are  transmitted  from  the  drum  to  the  in- 
ternal ear.  In  the  thickest  portions,  they  possess  Haversian 
systems.  Their  articular  surfaces  are  covered  by  hyalin 
cartilage.    The  stapes  alone  possess  a  marrow  cavity. 

The  MEMBRANE  clo'sing  the  fenestra  rotunda,  that  leads 
to  the  internal  ear,  consists  of  connective  tissue.  Its  middle 
ear  surface  is  covered  by  nonciliated  cells,  while  that  which 
lies  in  the  internal  ear  is  covered  by  endothelial  cells. 

The  OSSEOUS  portion  of  the  Eustachian  tube  is  lined  by 
a  thin  mucous  membrane  that  is  closely  adherent  to  the 
periosteum.     The  lining  cells  are  pseiido-stratiiied  ciliated 


THE  INTERNAL  EAR.  269 

elements.  Glands  are  absent.  In  the  cartilaginous  por- 
tion, the  mucosa  is  thicker,  and  is  lined  by  straiiHed  ciliated 
cells,  among  which  there  are  a  large  number  of  goblet  cells. 
In  the  tunica  propria,  mucous  glands  and  diffuse  lymphoid 
tissue  are  seen,  and  the  latter  may  be  formed  into  solitary 
follicles  near  the  pharyngeal  end. 

The  hlood  supply  to  the  tympanic  membrane  is  important. 
Its  external  surface  is  supplied  by  capillaries  derived  from 
the  vessels  of  the  external  canal,  while  the  inner  surface 
receives  vessels  from  those  of  the  middle  ear.  The  mucosa 
of  the  Eustachian  tube  receives  blood  from  both  the  middle 
ear  and  pharyngeal  vessels. 

Lymphatic  vessels  follow  those  of  the  circulatory  system.. 
Those  of  the  external  surface  of  the  membrana  tympani 
empty  into  those  of  the  external  canal,  while  those  of  the 
inner  surface  empty  into  those  of  the  tympanum.  The  latter 
lie  in  the  deeper  portions  of  the  tunica  propria,  and,  at 
intervals,  possess  dilatations. 

The  nerves  of  the  external  surface  of  the  tympanic  mem- 
brane are  derived  from  the  auriculo-temporal ;  in  addition 
to  these,  fibres  enter  at  the  edge.  Both  form  a  close  plexus. 
This  supplies  the  external  surface  by  a  subepithelial  plexus. 
The  inner  surface  is  supplied  by  the  tympanic  plexus,  which 
sends  branches  to  the  epithelial  layer.  Occasionally,  minute 
ganglia  are  present.  The  Eustachian  tube  receives  fibres 
from  the  tympanic,  as  well  as  from  the  pharyngeal  plexuses. 

THE  INTERNAL  EAR. 

The  Internal  Ear,  or  Labyrinth,  consists  oi  Sacculus, 
Utriculus,  Semicircular  Canals  and  Cochlea. 

The  Labyrinth  consists  of  the  osseous  and  membran- 
ous portions,  which  are  separated  from  each  other  by  a 


270  THE    EAR. 

lymph  space.  The  bony  labyrinth  surrounds  the  mem- 
branous portion,  and  is  separated  from  it  by  the  perilymph. 
Within  the  membranous  part  is  the  endolymph. 

SACCULUS    AND    UTRICULUS. 

'  The  Sacculus  and  Utriculus  are  two  cavities  of  unequal 
size,  which  do  not  communicate  with  each  other  directly, 
but  with  the  ductus  endolymphaticus  by  two  small  canals. 
The  Sacculus  is  the  smaller,  and  lies  anterior  to  the  utricu- 
lus. The  Utriculus  is  connected  to  the  semi-circular  canals, 
while  the  sacculus  communicates  with  the  cochlear  portion 
of  the  membranous  labyrinth,  by  means  of  the  ductus  re- 
uniens. 

The  bony  walls  are  covered  by  periosteum,  which  is  lined 
by  a  layer  of  endothelial  cells  continued  over  the  trabeculae, 
that  extend  from  the  periosteum  to  the  membranous  laby- 
rinth. From  this  point,  the  endothelium  continues  over  the 
external  surface. 

The  walls  of  the  saccule  and  utricle  are  composed  of 
bundles  of  white  fibrous  tissue  arranged  into  two  layers  of 
variable  thickness,  5  to  15  microns.  The  thickest  portions 
are  where  the  nerve  fibres  enter  the  maculae  acusticae  and 
maculae  cribrosae.  The  cells  lining  these  vesicles  consist 
of  simple  polygonal  epithelium,  3  to  4  microns  in  height, 
except  over  the  maculae  acusticae,  where  they  are  of  the 
neuro-epithelial  variety.  Upon  approaching  these  areas, 
the  polygonal  change  to  cuhoidal  and  become  progressively 
higher  until  a  height  of  30  microns  is  reached.  These  cells 
are  of  two  varieties,  sustentacular,  or  supportive,  and 

SPECIAL,    NEURO-EPITHELIAL,    Or   HAIR-CELLS. 

The  susTENTACULAR  cclls  are  very  long,  irregular  col- 
umns, the  basal  portions  of  which  are  branched.  The  large 
nuclei,  located  at  various  levels  in  the  inner  half  of  the  cell. 


THE  SEMICIRCULAR  CANALS.  27I 

produce  a  bulging  of  the  cell-body.  The  granular  proto- 
plasm possesses  pigment  granules  of  a  yellowish  color. 

The  special^  or  hair-cells,  are  also  columnar,  but  not  as 
long  as  the  preceding,  and  extend  through  only  one-half  of 
that  layer.  The  basal  portion  of  these  cells  is  broad,  and 
contains  large,  round  nucleus.  The  distal  end  is  rounded, 
and  possesses  a  cuticular  border,  the  cupola,  from  which 
projects  a  conical  cilium  120  microns  long.  This  ex- 
tends into  the  endolymph.  Closer  examination  shows  that 
the  cilium  consists  of  many  finer  hairs.  The  protoplasm  of 
these  cells  is  granular,  and  contains  a  yellowish  pigment. 

The  Otoliths  are  small,  prismatic  calcium  carbonate  crys- 
tals, I  to  15  microns  long,  occurring  in  the  vesicles,  and  im- 
bedded in  a  gelatinous  substance,  the  otolith  membrane, 
that  covers  the  neuro-epithelial  cells.  This  otolith  mcfii- 
hrane  contains  many  of  these  prisms. 

The  Ductus  Endolymphaticus  and  its  dilated  extremity, 
the  Sacculus,  have  the  same  structure  as  saccule  and  utricle. 

A  plexus  of  nerve  fibres  is  found  benea.th  the  neuro-epi- 
thelium.  The  fibres  extend  into  the  epithelial  layer,  and  as 
they  pierce  the  basement  membrane,  the  medullary  sheath 
blends  therewith,  and  leaves  the  axis  cylinder  free.  These 
latter  form  fibrillae  that  pass  to  the  neuro-epithelial  (hair) 
cells ;  some  pass  higher  between  the  supportive  cells. 

In  these  areas,  the  capillary  plexuses  are  especially 
numerous. 

THE  SEMICIRCULAR  CANALS. 

The  Membranous  Semicircular  Canals  are  united  to 
the  periosteum  by  trabeculae,  as  in  the  preceding,  and 
the  endothelial  ceils  pursue  the  same  course  in  this  lymph 
space.  The  epithelium  resembles  that  of  the  saccule  and 
utricle,  being  polygonal,  but  slightly  larger,  varying  from 


2^2.  THE    EAR. 

12  to  i6  microns.  Specialized  areas,  cristas  acusticae, 
are  found  in  the  floor  of  the  ampullae  (dilated  portions  at 
the  junctions  of  the  canals).  Here  the  thickened  fibrous 
wall  forms  the  transverse  septum.  The  specialized  areas 
resemble  those  of  the  saccule  and  utricle.  The  hairs  of  the 
neuro-epithelial  cells  are  unusually  long*,  some  reaching  to 
the  middle  of  the  lumen.  They  are  called  the  auditory 
HAIRS,  and  arise  from  the  cupola  of  the  cdls. 

The  nerve  fibres  pass  to  the  thick  transverse  septum, 
and  form  a  plexus  from  which  finer  fibres  follow  the  same 
course  as  in  the  saccule  and  utricle. 

The  blood-vessels  are  distributed  in  the  same  manner. 

THE  COCHLEA. 

The  Cochlea  consists  of  a  spiral  bony  canal  that  winds 
around  the  central,  vertical  axis,  or  modiolis.  The  bony 
canal  is  separa.ted  into  an  upper,  the  scala  vestibuli,  and  a 
lower,  the  SCALA  tympani.  These  divisions  are  further 
separated  by  a  central  shelf  of  bone  called  the  lamina  spir- 
alis. This  extends  about  half  of  the  way  across,  and  the 
BASILAR  MEMBRANE  Completes  the  partition.  At  the  upper 
end  of  the  cochlea,  these  canals  communicate  with  each 
other;  both  contain  the  perilymph. 

The  Ductus  Cochlearis,  or  Scala  Media,  is  a  delicate, 
triangular  canal  that  lies  in  the  scala  vestibuli;  its  outer 
basal  angle  is  attached,  externally,  to  the  outer  wall,  and  the 
inner  ang^le,  internally,  to  the  lamina  spiralis.  It  contains 
the  endolymph,  and  has  an  important  epitheHal  lining.  The 
BASILAR  MEMBRANE  Separates  it  from  the  scala  tympani. 
and  the  membrane  of  Reissner  from  the  scala  vestibuli. 
The  latter  membrane  is  quite  thin,  about  3  microns,  and 
extends  from  the  lamina  spiralis  (internal  to  the  crista)  to 
the  bony  wall  of  the  scala  vestibuli  at  an  angle  of  about  45 


THE    COCHLEA. 


nz 


degrees 


Upon  its  VESTIBULAR  WALL,  it  is  covered  by  a  layer 
of  pigmented  endothelial  cells  which  rest  upon  the  middle 
connective  tissue  layer,  in  which  capillaries  are  found.  The 
epithelial  lining  of  its  inner  surface  consists  of  a  single  layer 
of  polygonal  cells.  The  outer  wall  of  the  scala  media,  for 
about  two-thirds  of  its  distance  from  the  upper  angle,  is 
covered  by  ciihoidal  cells,  within  which  there  are  quite  a 


Fig.  91. — Horizontal  Section  through  Petrous  Bone  of  a  Kitten 
{Stohr's  Histology), 

1.  Ganglion  spirale ;  2.  macula ;  3.  ganglion  vestibulare  :  4.  meatus  acus- 
ticus  internus;  o.  vestibular,  and  6.  cochlear  divisions,  respectively, 
of  the  acoustic  nerve  ;  7.  scala  tympani ;  8.  scala  vestibuli ;  9.  bone ; 
10.  modiolus. 


number  of  capillaries,  a  very  unusual  conditian.  This  is 
the  stria  vascularis.  At  the  lower  margin  of  the  latter 
is  a  small  projection,  the  prominentia  spiralis;  this,  with 
the  lower  part  of  the  outer  wall,  is  covered  by  flattened  cells 
that  become  columnar  as  the  basilar  membrane  is  reached. 
The  tissue  external  to  these  cells  is  quite  thick,  and  extends 
over  the  vestibular  wall  above  the  attachment  of  Reissner's. 


274 


THE   EAR. 


membrane,  and  below  the  attachment  of  the  basilar  mem- 
brane. This  is  the  ligamentum  spirals.  At  the  attach- 
ment of  the  basilar  membrane,  this  ligament  forms  a  pro- 
jection called  the  crista  basilaris. 

The  FLOOR  of  the  ductus  cochlearis  (tympanic  side)  con- 


f    g 


Fig.  92. — Scheme  of  the  Structure  of  the  Tympanic  Wall  of  the 
Duct  of  the  Cochlea  {Stdhr^s  Histology), 

A.  Side  view ;  B.  surface  view.  a.  auditory  teeth  ;  b.  epitlielium  of  sulcus 
spiralis ;  c.  inner  hair  cells ;  d.  inner  head  plates ;  e.  outer  head 
plates ;  f.  phalanges  ;  g.  outer  hair  cells ;  h.  cells  of  Hensen  ;  i.  cells 
of  Claudius.  1.  Nerve ;  2.  first  spiral  cord ;  3.  inner  pillar  cells ; 
4.  vas  spirale ;  5.  tunnel  ;  6.  outer  pillar  cells ;  7.  Nuel's  spaces ; 
8.  Deiter's  cells  ;  9.  membrana  bisilaris ;  10.  tympanal  lamella. 


sists  of  the  basilar  membrane  that  unites  the  spiral  promi- 
nence to  the  spiral  lamina;  this  is  completed  by  the  ltmbus 
that  extends  from  the  end  of  the  spiral  lamina  to  the  attach- 
ment of  Reissner's  membrane. 

The  outer  portion  of  the  limbus  is  thicker  near  the  mem- 
brane, due  to  an  increase  in  the  periosteum.     This  portion 


THE  ORGAN  OF  CORTI.  275 

contains  clefts  and  depressions  that  deepen  toward  the  inner 
half,  at  which  point  the  cleft  is  quite  deep,  and  little  projec- 
tions, separated  by  lateral  clefts,  give  rise  to  the  auditory 
TEETH,  which  number  about  2,500.  These  teeth  and  pro- 
jecting areas  are  covered  by  simple  polygonal  cells,  while 
the  CLEFTS  are  lined  by  columnar  elements.  The  inner  half 
of  the  LiMBUS  consists  of  a  slightly  projecting  mass,  the 
SUPERIOR  LIP,  due  to  the  sudden  decrease  in  thickness,  and 
a  lower  portion  that  continues  over  the  bony  lamina  toward 
the  basilar  membrane ;  the  latter  is  the  inferior  lip.  Be- 
tween these,  lies  a  little  space,  the  sulcus  spiralis,  due  to 
the  sudden  decrease  in  thickness  of  the  periosteum.  The 
sulcus  is  lined  by  flat  cells. 

The  BASILAR  MEMBRANE  is  covcrcd,  on  its  tympanic  sur- 
face, by  the  tympanic  lamella,  made  up  of  spindle-shaped 
cells  and  delicate  fibres,  representing  an  incomplete  change 
to  endothelial  cells.  This  is  continuous  with  the  periosteum 
of  the  scala  tympani.  Above  this  layer  is  the  membrana 
propria,  that  represents  a  greatly  hypertrophied  basement 
membrane  and  seems  to  support  the  epithelium  upon  its 
upper  surface.  The  outer  end  of  the  basilar  membrane  is 
covered  by  the  cells  of  Claudius  that  continue  toward  the 
outer  wall  and  pass  into  the  columnar  and  flattened  elements 
that  are  found  upon  the  basilar  crest.  These  cells  possess 
spherical  nuclei  embedded  in  a  slightly  granular  and  pig- 
mented protoplasm;  they  represent  a  continuation  of  the 
CELLS  OF  Hensen.  Between  the  limbus  and  the  cells  of 
Claudius,  lies  the  organ  of  Corti,  composed  of  neuro-epi- 
thelial  and  sustentacular  cells.  This  organ  is  divided 
into  an  inner  portion,  the  membrana  tectoria,  and  an  outer 
part,  the  zona  pectinata. 

The  CELLS  of  the  Organ  of  Corti  are  the  pillar,  hair  and 
sustentacular  cells. 


276 


THE    EAR. 


The  PILLAR  CELLS  are  peculiar,  S-shaped  elements  pos- 
sessing a  striated  body,  surrounded  by  a  narrow  band  of 
protoplasm.  The  latter  is  thickened  at  the  base  (tunnel 
side),  and  in  this  part  is  seen  the  nucleus.  The  lower  end 
rests  upon  the  basilar  membrane,  and  is  expanded  to  form 


\ 

P 

Fig.   93. — Cokti's   Organ,     x  Tunnel  of  Corti  traversed  by  nerve 
fibres    {St6hr's   Histology). 

a.  Labium  vestibulare  ;  6.  sulcus  spiralis  ;  c.  membrana  tectoria ;  d.  inner 
hair  cells ;  e.  outer  hair  cells  ;  /.  cells  of  Hensen  :  g.  cells  of  Claudius ; 
h.  capillaries  of  stria ;  i.  nerve  bundle  ;  k.  labium  tympanicum  :  I.  in- 
ner pillar  cells  :  ni.  outer  pillar  cells  ;  n.  cells  of  Deiter ;  o.  membrane 
basilaris ;  p.  tympanal  lamella. 

the  FOOT ;  the  upper  end  likewise  undergoes  an  expansion, 
termed  the  head.  These  cells  form  two  rows,  inner  and 
outer;  they  articulate  above,  and  form  a  triangular  canal 
called  CoRTi's  tunnel.  This  contains  a  semi-solid  inter- 
cellular substance.     The  inner  cell,  being  shorter,  is  more 


THE  ORGAN  OF  CORTI.  2/7 

nearly  vertical,  and  its  head  bears  an  articular  surface  for 
the  reception  of  the  articular  head  of  the  outer  cell.  The 
inner  cells  are  more  numerous  and  thinner  than  the  outer, 
about  3,850  to  3,600,  respectively.  The  head  process  of 
both  cells  continues  externally  as  a  thin,  shelf-like  process 
called  the  head  plate.  Of  these,  the  inner  head  plates  lie 
above,  but  are  shorter  than  the  outer.  The  outer  are  called 
the  phlangeal  processes,  and  by  their  union  with  the  cells 
OF  Deiter,  form  the  membrana  reticularis. 

The  NEURO-EPiTHELiAL  CELLS  are  distributed  upon  the 
inner  and  outer  surfaces  of  the  pillar  cells.  They  are  the 
HAIR  CELLS,  and  of  these  there  are  two  rows,  inner  and 
OUTER.  Like  the  hair  cells  of  the  preceding,  and  the  neuro- 
epithelial cells  of  the  nasal  mucous  membrane,  they  are  about 
half  the  length  of  the  sustentacular,  or  pillar  cells,  and  are 
columnar  elements  containing  a  granular  protoplasm  and  an 
oval  nucleus.  The  outer  end  has  a  cuticular  border,  from 
which  about  twenty  hairs  extend.  The  outer  cells  are  longer 
and  narrower  than  the  inner,  and  more  numerous.  Usually, 
one  hair  cell  is  present  for  each  two  pillar  cells.  The  outer 
hair  cells  are  found  in  three  or  four  rows,  which  are  sep- 
arated by  the  ends  or  phalanges  of  Deiter's  cells  and  the 
membrana  reticularis.  The  inner  row  rests  upon  the  outer 
pillar  cells ;  the  cells  of  the  next  row  lie  opposite  to  the  rods, 
and  the  third  row  alternates,  producing  a  peculiar  checker- 
board appearance,  the  ends  of  the  hair  cells  being  separated 
from  one  another  by  the  ends  of  the  Deiter  cells. 

The  SUSTENTACULAR,  or  Deiter,  cells  are  internal  and 
EXTERNAL.  Each  ccll  consists  of  a  thin  pyramidal  process 
and  a  large  basal  part  that  contains  the  nucleus.  The  in- 
tercellular SPACES  OF  NuEL,  between  the  cells  of  the  organ 
of  Corti,  contain  a  substance  like  that  in  the  tunnel  of  Corti. 
Internally,  Deiter's  cells  pass  through  the  entire  layer,  and 
are  continuous   with  the  cells   of  the  sulcus.     Externally, 


278  THE    EAR. 

they  form  the  phalanges  that  help  produce  the  membrana 
reticularis.  A  surface  view  will  show  both  sustentacular  and 
neuro-epithelium ;  a  basal  view,  however,  will  show  only 
sustentacular  elements.  Just  external  to  the  Deiter  cells  are 
other  sustentacular  elements,  the  cells  of  Hensen.  These 
extend  to  and  continue  with  those  of  Claudius.  Extending 
over  the  organ  of  Corti,  and  arising  from  the  upper  lip  of 
the  limbus,  is  a  membrane  composed  of  delicate  fibres  and 
interfibrillar  substance.  This  is  the  membrana  tectoria^ 
or  CoRTi's  MEMBRANE.  ^At  One  time,  this  was  part  of  the 
cells  beneath,  those  of  the  sulcus  and  auditory  teeth;  it 
represents  a  cuticular  border. 

The  branches  of  the  auditory  nerve  are  vestibular  and 
cochlear.  The  vestibular  supplies  the  sacculus,  utriculus, 
maculae  and  the  semicircular  canals  (cristae).  The  coch- 
lear branch  passes  to  the  cochlea,  and  is  made  up  as  follows : 

In  a  little  bony  canal  in  the  lamina  spirale  is  a  strip  of 
gray  matter  that  is  called  the  ganglion  spirale.  This  con- 
sists of  bipolar  cells,  one  branch  of  which  passes  outward 
into  the  organ  of  Corti,  while  the  other,  the  axis-cylinder, 
passes  through  a  minute  canal  in  the  axis  to  the  central 
canal,  where  it  meets  other  fibres  from  different  levels. 
These  pass  to  the  base  and  to  the  internal  auditory  meatus, 
as  the  COCHLEAR  BRANCH,  and  then  to  the  medulla.  The 
dendritic  branches  of  these  ganglion  cells  form  a  plexus  in 
the  minute  canal  of  the  spiral  s'helf.  Toward  the  organ  of 
Corti,  the  lamina  is  pierced  by  many  canals  called  the  for- 
amina NERVOSA,  through  which  numerous  fibres  pass,  along 
its  inner  epithelium,  to  the  organ  of  Corti.  Upon  entering 
these  canals,  the  medullary  sheaths  and  neurilemmae  are  lost, 
and  the  naked  axis-cylinders,  in  bundles,  continue.  Each 
bundle  separates  into  two,  one  of  which  remains  at  the 
inner  surface,  and  the  other  passes  along  the  outer  side  of  the 
pillar  cells.    The  latter  lies  in  the  tunnel.    Other  fibres  cross 


THE   CIRCULATION   OF   THE   EAR.  279 

the  tunnel  and  pass  to  the  outer  side  of  the  outer  pillar  cells 
and  form  several  bundles  between  the  Deiter  cells.  From 
these,  various  bundles,  fibrillae  end  upon  the  hair  cells. 

The  blood-vessels  follow  the  nerves,  those  of  the  utriculus 
and  sacculus  follow  the  vestibular  branch,  and  those  of  the 
cochlea  the  cochlear  division.  After  giving  off  branches  to 
the  first  turn,  the  main  trunk  enters  the  canal  of  the  axis, 
from  which  the  branches  form  the  peculiar  glomeruli 
COCHLEAE.  Branches  of  the  latter  penetrate  the  scala  vesti- 
buli,  and  supply  the  limbus  and  neighboring  tissues.  Other 
branches  continue  over  the  vestibule  to  the  ligamentum 
spirale,  the  stria  vasculare,  and  basillar  membrane  surround- 
ing the  scala  vestibuli.  The  veins -surround  the  scala  tym- 
pani  and  form  a  trunk  below  the  spiral  ganglion. 


CHAPTER  XX. 


THE  SENSES  OF  SMELL,  TASTE 
AND  TOUCH. 


THE  ORGAN  OF  SMELL. 

The  Nasal  Mucosa  is  divided  into  respiratory  and  ol- 
factory portions.  The  lowF^r  portion  of  the  respiratory 
area,  called  the  vestibule^  is  lined  by  stratified  squamous 
cells  to  the  inferior  turbinate  bone.  Here  a  great  many 
hairs,  sebaceous  and  mucous  glands  that  extend  for  a  short 
distance,  are  encountered.  Above  the  turbinate,  the  epithel- 
ium is  of  the  stratified  ciliated  variety,  and  many  goblet  cells 
are  present.  The  tunica  propria  contains  much  adenoid  tis- 
sue and  a  large  venous  plexus.  Mucous  and  serous  glands 
are  also  present  in  great  numbers  in  the  region  of  the  inferior 
turbinate  and  nasal  septum.  The  mucosa  is  4  mm.  thick 
in  this  area. 

The  OLFACTORY  mucosa  is  usually  prominent  on  account 
of  its  yellow  color,  but  this  does  not  indicate  the  entire  ol- 
factory membrane.  It  is  very  thick,  and  ciliated  cells  no 
longer  exist.  The  epithelium  is  of  the  neuro-epithelial  var- 
iety, and  two  kinds  are  present,  the  sustentacular  and 

NERVOUS  elements. 

The  SUSTENTACULAR  cells  are  irregular,  and  possess  an 
OUTER  SEGMENT  which  is  Cylindrical,  and  an  inner  that  is 
narrow  and  irregular.  The  outer  segments  form  a  row  of 
columnar  elements.  The  oval  nuclei  form  a  regular  band 
or  row.  The  protoplasm  contains  granules  and  pigment 
near  the  inner  end,  the  former  being  arranged  in  rows.  A 
cuticular  border  is  present,  and  forms  the  membrana  lim- 

280 


THE  NASAL   MUCOSA.  281 

ITANS  OLFACTORiA.     The  inner  segments  are  irregular,  and 
usually  branch  at  their  internal  ends. 

The  NERVOUS  ELEMENTS,  GT  neuro-epithelial  cells  proper, 
consist  of  a  peculiar,  inconspicuous  strips  of  protoplasm  pos- 
sessing an  enlargement  near  the  middle,  in  which  lies  a 
large,  round  nucleus.  The  latter  form  a  band  or  zone  of 
spherical  elements.  The  outer  end-s  of  the  rods  extend  to 
the  free  surface,  between  the  supportive  cells,  while  the 
inner  ends  pass  to  the  basement  membrane. 


Pig.  94. — Diagram  of  Olfactory  Mucosa. 

a.  Sustentacular  cells ;  &.  neuro-epithelial  elements ;  c.  basal  cells ;  d,  base- 
ment membrane. 


The  BASAL  cells  are  small  and  irregular  elements  that  send 
processes  between  the  upper  layers  and,  internally,  rest  upon 
the  basement  membrane. 

The  tunica  propria  consists  of  a  loose  network  of  fibro- 
elastic  tissue.  This  supports  the  mucous  (Bowman's) 
glands,  whose  functionating  epithelium  possesses  a  brownish 
pigment.  These  glands  are  numerous,  forming  a  continuous 
layer. 

The  Accessory  Cavities  possess  a  lining  of  ciliated  cells. 
The  mucosa  is  very  thin,  .02  mm.,  and  it  is  firmly  attached 
to  the  perio'Steum.  Glands  are  very  few  in  the  mucosa  of 
these  cavities. 


282 


THE  SENSE  OF  SMELL. 


The  blood-vessels  are  numerous.  The  arterial  branches 
form  a  dense  subepitheHal  plexus,  including  a  network 
around  the  glands.  The  veins  are  large  in  number  and  size, 
especially  upon  the  inferior  turbinate. 

The  lymphatics  lie  in  the  lower  part  of  the  tunica  propria ; 
in  the  olfactory  area,  an  extra  set  of  vessels  occurs  in  the 
superficial  portion.  These  communicate  with  the  channels 
around  the  nerves. 


fis 


Fig.  95. — Isolated  Elements  of  the  Olfactory  Mucosa. 
a.   Neuro-epltlielial   cell ;    &.  sustentacular  cells  showing  cuticular  border. 


The  nerves  are  those  of  ordinary  and  special  sensation. 
The  former  are  derived  from  the  trigeminus,  and  do  not  pass 
to  the  cells.  The  tatter  are  derived  from  the  olfactory  nerve. 
The  fibres  of  the  olfactory  nerve  are  nonmedullated,  and  are 
sent  from  branches  that  lie  between  the  mucosa  and  the 
bony  wall.  These  pass  to  the  epithelial  layer,  and  are  sur- 
rounded by  perineural  lymphatic  sheaths.  When  the  epi- 
thelium is  approached,  the  fibres  break  into  ultimate  fibrillae 
that  pass  directly  to  the  neuro-epithelial  cells.  The  central 
ends  of  these  fibres  are  in  relation  with  the  glomerular  cells 
of  the  olfactorv  lobe. 


THE  SENSE  OF  TASTE.  283 

THE   SENSE   OF  TASTE. 

The  Sense  of  Taste  is  clue  to  the  Taste-buds. 
These  are  not  restricted  to  the  circitmvallate  papillae  of  the 
tongue,  but  are  found  in  the  papillae  foliatae,  in  the  posterior 
surface  of  the  epiglottis,  at  times  in  the  fungiform  papillae 
and  in  the  soft  palate  and  uvula. 

The  organs  are  barrel-shaped,  and  consist  of  two  varieties 
of  cells,  the  sustentacular  and  the  neuro-epithelial. 

The  sustentacular  cells  are  the  outer,  and  are  com- 
posed of  a  cell-body  and  a  pointed  end.    The  latter,  with  its 


2,  __;..,  ~;a;vC-l- 


Fig.  96. — Taste-bud  from  a  Papilla  Foliata  of  a  Rabbit. 

1.    Epithelium ;    2.    tunica    propria ;    a.    taste-bud ;    b.    gustatory    hairs ; 
c.  gustatory  pore. 

neighbors,  forms  an  opening  at  the  exposed  end  of  the  organ 
called  the  gustatory  pore.  The  cell-body  varies  in  its  thick- 
ness and  the  enlargement  may  be  central  or  proximal.  In 
this  enlargement  is  seen, the  large  nucleus. 

The  NEURO-EPITHELIAL  elements  are  peculiar,  long, 
spindle-shaped  cells  possessing  a  nuclear  enlargement.  This 
is  more  pronounced  than  that  of  the  preceding.  The  peri- 
pheral end  of  each  cell  is  continued  as  a  hair-like  projection 
through  the  gustatory  pore;  this  projection  is  the  gustatory 

HAIR. 

The  GLOSSO-PHARYNGEAL  NERVE  forms  a  plexus  in  the 
tunica  propria,  and  from  this,  a  subepithelial  plexus  arises. 


284  THE  SENSE  OF  TOUCH. 

From  the  latter,  fibres  pass  to  the  taste-buds,  some  to  enter 
and  others  to  surround  this  Httle  organ.  Those  that  enter, 
surround  the  gustatory  cells  in  a  deHcate  plexus,  and  end 
as  little  enlargements  upon  the  cells.  The  other  fibres  form 
branches  in  the  epithelium  between  the  taste-buds,  termi- 
nating in  end-bulbs. 

THE  SENSE  OF  TOUCH. 
The  Sense  of  Touch  is  not  limited  to  any  special  region, 
but  it  is  best  developed  in  certain  areas,  as  the  palm  and 
SOLE.     It  is  restricted  to  the  skin,  and  represents  a  modifi- 


FiG.   97. — Corpuscle   of   Meissner  from   Great   Toe   of   Man. 
n.    Medullatea    nerve   Gbre ;    n.    connective    tissue   sheath ;    e.   varicosities. 
The  nuclei  are  invisible  {Stohr^s  Histology). 

cation  of  general  sensibility.     In  the  papillae  of  the  skin, 
especially  that  of  the  sole  and  palm,  are  found  the  tactile 

CORPUSCLES    OF    MeISSNER. 

These  are  elongated  structures,  about  50  by  150  microns, 
and  possess  transverse  striations  that  seem  due  to  cells  with 
transversely  placed  nuclei.  These  are  encapsulated  by  white 
fibrous  tissue,  and  are  pierced,  at  the  lower  end,  by  nerve 
fibres  whose  medullary  sheaths  blend  with  the  capsule.  The 
axis  cylinders  run  spirally,  branch  within  the  organ  and  in- 


PACINIAN    BODIES. 


285 


terlace.  These  branches  are  irregular,  and  possess  enlarge- 
ments, at  intervals. 

The  corpuscles  of  Vater,  or  Pacinian  bodies,  are  very 
large,  oval  structures.  Each  consists  of  a  capsule,  an  inneu 
BULB  and  an  end-knob. 

The  CAPSULE  consists  of  many  layers  of  white  fibrous  tis- 
sue, each  separated  from  its  neighbor  by  a  lymph  space  lined 


Fig.    98. — Pacinian   Body   from   Mesentery   op   a   Cat. 
1.   Fat   cells ;  2.  artery ;    3.   nerve  fibre ;   4.   inner  bulb ;    5.   axis-cylinder ; 
6.    layers  of  the   capsule    {Stohr's  Histology). 


by  endothelial  cells.  These  lamellae  are  held  together  by 
an  INTRA-CAPSULAR  LIGAMENT  that  pierces  all.  The  inner- 
bulb  is  a  cylindric  mass  of  almost  homogeneous  protoplasm 
possessing  nuclei.  Through  this,  the  axis  cylinder  passes 
to  terminate  in  a  slight  enlargement  called  the  end-knob. 

The  conjunctival  corpuscles,  or  corpuscle  of  Krause, 
are  also  tactile  corpuscles.  These  are  surrounded  by  a  deli- 
cate  fibrous   capsule,   which   is   surrounded   and   lined   by 


286  THE  SENSE  OF  TOUCH. 

endothelium.  The  center  of  the  corpuscle  seems  occupied 
by  the  divisions  of  the  axis  cylinder  that  passes  to  it,  and 
by  lymph.  Such  corpuscles  are  found  in  the  conjunctiva, 
edges  of  the  eyelids,  in  the  lips,  epiglottis,  and  in  the  glans 
penis  and  glans  clitoris. 

The  GENITAL  CORPUSCLES  are  more  complex  than  the  pre- 
ceding. They  may  resemble  the  Pacinian  body,  or  may  be 
composed  of  several  simple  corpuscles  fused  into  one. 


INDEX. 


A. 

Accessory  cavities,  281 
Acervulus  cerebri,  232 
Achromatic  spindle,   35 
Achromatin,   30 
Acid  cells,    14,    119 
Acidophil,  see  Eosinophil 
Acrosome,   173 
Adamantoblasts,    107 
Adelomorphous  cells,    118 
Adenoid  tissue,    59 
Adipose  tissue,  58 
Adrenal,   166 
Adventitia   of   artery,    90 

of  vein,  94 
Agminated   follicles,   60,    126 
Air-sacs,   149 
Albumen,  Mayer's,  25 
Alcohol     for     clearing,     absolute     and 
ether,   8 

for  fixation,   absolute,  4 

absolute  and  ether,    5 

absolute  and   formalin,    5 

ninety-five  per  cent.,   4 
Alimentary   tract,    106 
Allantois,  201 
Alum  carmin,    15 
Alvei,   147 
Alveolar  ducts,    148 

membrane,    no 
Alveoli  of  lungs,    149 
Alveolo-tubular   glands,    50 
Amakrine  cell,  256 
Ameboid  motion   of  leukocytes,   96 
Amelioblasts,    107 
Amitosis,    33 
Ammion,   false,  200 

true,   205 
Ammiotic  cavity,   199 

folds,  200 
Amphipyrenin,   30 
Ampullae 

capillary,    92 

of  ear,  272 

of  oviduct,    188 

of  spleen,    103 
Amyloid  bodies,    175 
Anabolism,  31 
Anaphase,    36 
Anastomoses,    93 
Angle  of  infiltration,  252 
Angles,  leaden,   7 
Anilin   oil-xylol,    20 
Anisotropic  disc,   ^2 
Annuli  fibrosi,   88 
Annulus  fibrosus,  268 
Antrum  of  follicle,    183 
Appendix,  follicles  of,   128 

glands  of,   128 

occlusion  of,   129 
Aqueous  humor,  258 


287 


Arantii,   corpus,    89 

Arachnoid,   226 

Arcuate  fibres  of  the  cornea,  246 

of  the  pons,  236 
Arcus  tarseus  externus,  265 

internus,    265 
Area  of  Langerhans,   134 
Areola,   224 
Areolar  tissue,  58 
Arrectores    pilorum,    218 
Arteries,  large,   91 

medium,  90 

small,   92 
Astrosphere,    30 
Atria,    149 

Attraction  sphere,  30 
Auditory  cells,   2Tj 

hairs,  2^^ 

nerve,  278 

ossicles,  268 

teethj   275 
Auerbach,  plexus  of,   130 
Axial  fibre,   173 
Axis-cylinder,  78 
Axilemma,  80 

B. 

Basal  border,   128 

Balsam,   20 

Basement   membrane,   46 

Basic  stains,    12 

Basilar  membrane,   2T2 

Basket  cells,   22,2 

Basophil,   97 

Belly-stalk,    201 

Bensley's  solution,   3 

Benzol,   7,  20 

Berlin  blue.   22 

Bertini,    columns  of,    157 

Bile  capillaries,   133 

Biondi-Heidenhain  stain,    16 

Bipolar   cells,    79 

Bismark  brown,    13 

Bladder,   163 

Blastodermic   vesicle,    39 

Blastula,  39,   198 

Blind  spot,  257 

Blocking,    7 

Blood 

cells  of,  erythroblasts,  25,  95,  102 
erythrocytes,    94 
leukocytes,   96 
platelets,   25,   97 

crystals,   98 

films,  23 

fixation,    5 

hemoglobin,  98 

platelets,   25,   97 

technic,  fixation,   2^ 
spreads,    23 
stains,  2^,  24 


288 


INDEX. 


Blood-forming  organs 

carotid  gland,  99 

coccygeal  gland,  99 

marrow,  67 
Blood-vessels 

arteries,    90 

capillaries,    92 

heart,   89 

nerves  of,  94 

veins,   93 
Bone 

canaliculi,  dy 

cells,   64 

compact,   65 

composition,   64 

corpuscles,   65 

decalcification,   64 

development 

endochondral,    68 
intramenbranous,  71 
growth,   71 

Haversian   canal,   dd 
lamellae,   dd 
system,   dd 

Lacunae,  dd 

Howships,   66 

lamellae,   65 

lymphatics  of,   68 

marrow  cavity,   67 
cells,    68 
red,   dy 
yellow,    67 
nerves  of,   68 

osteoblasts,    65 

osteoclasts,   65 

perichondral,  69 

periosteum,  64 

Sharpey's,    fibres  of,    64 

structure  of,  65 

Volkmann's  canals,    dd 

vessels  of,   68 
Bone-cells,   64 
Bone-marrow 

cells  of,    67 

red,  dy,  68 

serous,   67 

yellow,  67 
Bones  of  ear,  268 
Bony   cochlea,    2^2 

labyrinth,    269 
Borax   carmin,    14 
Boundary  zone  of  choroid,   248 
Boundary  zone  of  kidney,    159 
Bowman's  capsule,    156 

glands,    281 

membrane,  246 
Brain,  see  Cerebrum 
Brain  sand,   22,2 
Bronchi,    146 
Bronchiole 

respiratory,   148 

terminal,    148 
Bruecker's  lines,  72 
Brunner's  glands,    126 
Bulb,   hair,   215 
Bulbus  oculi,  see  Eyeball 
Burdach's  columns,  242 


C. 

Cecum,  foramen,  1 1 1 
Cajal,  cells  of,  229 
Calcification  of  cartilage,  69 
Calyces,  renal,  161 
Cambium  layer,  71 
Canada  balsam,  20 
Canal,    hyaloid,   258 

of  Petit,    259 

of   Schlemm,    251 

of    Stilling,    258 

of  spinal   cord,   240 

semicircular,  271 
Canaliculi,   of  bone,  dy 

of  eyelid,   266 
Canalized  fibrin,  206 
Capillaries,   bile,    133 

blood,   92 

lymph,    100 

secretory  of  acid  cells,    120 
of    demilunes,    140 
of   hepatic   cells,    134 
of    parotid,    139 
Capsule 

of  Bowman,    156 

of    cartilage    cells,    261 

of  Glisson,   132 

of   lens,    258 

of  Tenon,  266 

suprarenal,    166 
Carbol-xylol,  20 
Cardia,    118 
Cardiac  muscle,   76 
Carmin,   borax,    14 

alum,    15 

injection   mass,    22 
Carminic  acid,    15 
Carotid   gland,   99 
Cartilage 

calcification  of,   69 

capsule,   62 

cells,   61 

chrondroblasts,    61 

costal,   62 

elastic,    62 

fibro,   d2 

hyalin,  62 

ossification    of,    69 

perichondrium,    61 

vessels  of,   63 
Caruncle,    lacrimal,   265 
Cedar   oil,    5,    20 
Cellodin  infiltration,    8 
Cells 

acid,    14,    119 

acidophilic,    96 

adelomorphous,    118 

amakrine,   256 

auditory,   2t^ 

basket,   232 

basophilic,    97 

bipolar,    79 

blood 

red,   94 
white,   96 

bone,  d<i 


INDEX. 


289 


Cells  (continued) 
Cajal,   229 
cartilage,    61 
centro-acinar,    139 
chief,    118 
chromatophilic 

adrenal,    166 
ciliated,  44 
Claudius,  275 
columnar,  43 
cone-visual,    253 
connective  tissue,   53 
crystals  (eye),  248 
decidual,  206 
definition  of,   28 
Deiter's,    79,   2^7 
delomorphous,    118 
demilunar,    140 
^ZZ,  37 

ectodermal,   199 
enamel,    107 
endothelial,   46 
entodermal,   199 
ependymal,    240 
epithelial,   241 
eosinophil,    96 
fat,   59 
form,  31 
follicular,    184 
ganglion,  82 
giant,  37 
glia,  79 

glycogen   in,    29 
goblet,   44 

granule    (cerebellum),    234 
Golgi,  79 
gustatory,  283 
hair,  271,  277 
Hensen's,   275 
hepatic,    133 
interstitial 

of  ovary,    188 

of  testicle,    172 
Langhans,   203 
liver,    133 
lutein,   187 
marginal,   238 
marrow,  67 
mast,  97 
mesothelial,  46 
mitral,  231 
mossy,   79 
mother,    174 
mucin,   44,    122 
multipolar,   79 
''    muscle 

cardiac,    76 

smooth,   75 

voluntary,    72 
nerve,   78 

neuro-epithelial,  44 
neuroglia,   79 
of  Claudius,  275 
of  Clark's  column,  240 


Cells  (continued) 
of  Golgi,   79 
of  Hensen,  275 
of  Langerhans,   39 
of  Langhans,  203 
of  Leydig,   172 
of   Purkinje,   232 
of  Sertoli,   171 
olfactory,   281 
oxyntic,    118 
parietal,   119 
peptic,   118 
pigmented,   45 
pillar,   276 
plasma,    55 
polymorphous,    229 
polynuclear,  96 
prickle,  44,  211 
properties  of,  31 
pseudostratified,   43 
pyramidal 

large,  228 

small,   228 
reproduction  of,  32 
rod-visual,   254 
seminiferous,    171 
sexual 

fertilization,    38 

maturation,  37,    186 
shape  of,  31 
size  of,   31 
spider,   79 
squamous,  42 
stain  reaction  of,  29 
structure  of,  28 
stellate  bone,  64 

connective  tissue,   53 

nerve,  238 
sustentacular 

of  ear,  270,  277 

of  olfactory  membrane,  280 

of  retina,  254 

of  taste-bud,    iii,  283 
tactile,    83 
tendon,   57 
transitional,   45 
trophodermal,    199 
wandering,   53 
Cell-body,    28 
Cell-division 

amitosis,  33 
mitosis,   3s 
time  of,   37 
Cell-knots,   204 
Cell-mass,    inner,    39,    198 

outer,    39,    198 
Cell  membrane   (wall),   31 
Celloidin 

casting,  9 
hardening,   9 
infiltration,    8 
sectioning,    10 
solutions,   8 
Cell-spaces  of  Nuel,  277 
Cementum,   108 


290 


INDEX. 


Central  artery  of  retina,   259 

nervous   system,   226 

spindle,    35 
Centro-acinar   cells,    139 
Centrosomes,   30 
Cerebellar   columns,   direct,   242 

cortex,   2^2 

basket  cells  of,   2:^2 

capillaries  of,  243 

cells  of  Purkinje,   2^2 

ganglionic  layer,  2^2 

granule  layer,   234 

medullary  substance,  234 

molecular  layer,    2:^2 

neuroglia,   234 
Cerebral   cortex,   228 

capillaries  of,   243 

cells  of  Cajal,  229 

medullary  substance,   229 

molecular  layer,  229 

neuroglia   of,   227 

polymorphous  cells  of,    229 

pyramidal  cells  of,  228 

radial  bundles,  229 

tangential    layer   of,    229 
Ceruminous   glands,    267 
Cervix,    190 
Chambers 

anterior,   259 

posterior,   259 

vitreous,   259 
Chief  cells,    118 
Chloroform  for  clearing,   6,  7 
Chorda  tendineae,  88 
Chorio-capillaris,    249 
Chorion,   202,   205 

frondosum,  203 

laeve,    203 

primitive,  200 
Chorionic  villi,   203 
Choroid  coat 

arteries  of,   261 

boundary  zone,   248 

glassy  membrane,  249 

lamina  vasculosa,   249 

stroma  of,  247 

tapetum  cellulosum,   248 
fibrosum,    248 
Chromatic  spindle,   36 
Chromatin,   30 
Chromosomes,    34 

number  of,  34 
Chyli,   receptaculum,    130 
Cilia  of  eyelid,   234 
Ciliary  body,  249 

muscle,   250 

processes,   249 

ring,    249 
Ciliated   cells,   44 
Circulus  iridicus  major,   261 

minor,   261 
Circulatory  system,   88 
Circumferential   lamellae,   65 
Circumvallate   papillae,    1 1 1 
Cistern  of  Piquet,   130 


Clark,   column   of,    242 
Claudius,   cells  of,   275 
Clitoris,   196 
Coccygeal  gland,  99 
Cochlea 

bony,   272 

perilymph,  272 
Cochlea 

spiral  ganglion  of,   278 
Cohnheim's  fields,  7:^ 
Coiled   glands,    50 
Colloid  substance,   151,   153,  231 
Colostrum   corpuscles,    223 
Columns 

antero-lateral,    242 

antero-median,  240 

ascending,  242 

cerebellar,   242 

descending,    242 

lateral,  242 

mixed,   242 

of  Bertini,    157 

of  Burdach,  242 

of  Clark,   240 

of  Goll,  242 

of  Gower,  242 

of  Lissauer,    243 

of  Sertoli,   171 

pyramidal,    direct,    242 
crossed,  242 
Commissure,    gray,    238,    240 

white,    240 
Compact  bone,    65 
Cone-fibres,  253 
Cone-granules,   254 
Coni  vasculosa,   171 
Conjunctiva 

corpuscles  of,   83,   285 

palpebral,   264 

scleral,  245 
Connective   tissues 

adipose,   58 

adenoid,  59 

areolar,    58 

blood,  71 

bone,   63 

cartilage,  61 

cells  of,   53 

classification  of,   53 

dentin,    71 

elastic,   57 

embryonic,    57 

fibrous,   55 

ifitercellular  substance   of,    55 

modified,    50 

mucous,   57 

origin  of,    55 

reticulum,    58 

retiform,   58 

varieties  of,    53 
Conus   medullaris,    2^7 
Convoluted  tubules  of  kidney,    157 
Cord,  umbilical,  208 
Cords,   medullary,    10 1 


INDEX. 


291 


Corium,  212 
Cornea,  245 
Corneal   corpuscles,   246 

lacunae,   246 
Corneo-scleral  junction,  251 
Corona  radiata,    183 
Corpora   cavernosa,    180 
Corpus   albicans,    187 

Arantii,   83 

hemorrhagicum,    186 

Highmori,    169 

luteum   spurium,    187 
verum,   187 

spongiosum,    180 
Corpuscles 

blood,  red,   94 
white,   96 

bone,   64 

colostrum,  22^ 

conjunctival,   83,   285 

corneal,  246 

genital,  83,  286 

Hassal's,    105 

Krause,   285 

lamellar,  84,  285 

Malpighian,    103 

Meissner's,   83,   284 

Pacinian,   84,    285 

renal,    156 

splenic,    103 

tactile,    83 

Vater,   83,   285 

Wagner,  83,  284 
Corrosive  sublimate  fixative,    i,  2 
Corti's 

membrane,   278 

organ,  275 

tunnel,   276 
Cover-glass,    27 
Cowper's  gland,    179 
Cotyledons,  205 
Creosote,    19 

Crescents  of  Gianuzzi,    140 
Crista   basilaris,    274 
Cristae  acusticae,   272 
Crossed   pyramidal   tract,    242 
Crown,    107 
Crusta  petrosa,    108 
Crypts,    gastic,    117 

Lieberkuehns,    122 

tonsiller,    113 
Crystalline  lens,  258 
Crystals 

hematoidin,   98 

hemin,  98 

hemoglobin,  98 

in  the  choroid,   248 

Teichmann's,    99 
Cumulus  ovigerus,    183 
Cup,   imbedding,    8 
Cupola,    271 
Cuticular   border,    122 
Cuticle  of  hair,  217 
Cutis  vera,    212 
Cystic  duct,    136 
Cytoplasm,   28 


D. 

Dammar,   21 
Daughter  cells,    174 

nuclei,   36 

stars,    36 
Decalcification,    1 1 
Decidua 

ovular,    18 

placental,    198 

reflexa,  198 

serotina,    198 

uterine,    198 

vera,    198 
Decidual  cell,  206 
Dehydration,    15 
Deiter's    cells,    79,    277 
Delafield's  hematoxylin,   12 
Delomorphous  cells,    118 
Demilunes  of   Heidenhain,    140,    141 
Dentin,   71,    109 
Dentinal  canals,    109 

fibres,    109 

tubes,   109 

sheaths,    109 
Derivatives  of  triploblast,  39 
Derma,   212 
Descending   columns,    242 

limb  of  Henle's  loop,    157 
Deutoplasm,   184 
Diaster,   ^^ 

Diffuse  adenoid  tissue,  60 
Digestive  glands,    132 
Dilator   pupillae,    251 
Diploblast,    39,    199 
Direct  cell-division,   33 

cerebellar  tract,   242 

pyramidal  tract,    242 
Discus  proligerus,    183 
Dobie's  globules,  y:^ 
Duct 

alveolar,    148 

Bartholin,   141 

cochlear,   272 

ejaculatory,    177 

endolymphatic,    271 

galachtophorous,   22^ 

pancreatic,    139 

Rivini,    141 

Steno's,    139 

Wharton's,    141 

Wirsungian,    139 
Duodenum,    126 
Dura,  226 

E. 

Ear 

external,   267 

internal,   269 

middle,   268 
Ear,   bones  of,   268 
Ear-stones,   271 
Ectoderm,   38,    199 

derivatives  of,  39 
Egg-tubes  of  Pflueger,    184 
Ehrlich-Biondi-Heidenhain    stain,    16 
Ehrlich,  fixation  of  blood,  2^ 


292 


INDEX. 


Ejaculatory  duct,    177 
Elastic  cartilage,  62 

lamina  anterior,   240 
internal,  90 
external,  90 
posterior,   247 
Elastin,  57 

Ellipsoidal   sheaths,    104 
Embedding   celloidin,    8 

paraffin,   6 
Embryonic  area,    198 

shield,    199 

tissue,   57 
Emissary   veins,    180 
Enamel,    107 

prisms,    107 
End-bulbs,    83 
End-knobs,   84,    173 
Endocardium,   88 
Endochondral   bone,   68 
Endolymph,   270 
Endomysium,    75 
Endoneurium,    82 
End-organ  of  Ruffini,  86 
Endothelial  cells,   46 

membrane,   46 
End-plate,   85 
Entoderm,  39,    199 

derivatives,    40 
Entodermal  vesicle,    199 
Eosin,    14 
Eosinophyl 

coarsely  granular,  96 

finely  granular,  97 
Ependymal  cells,  240 
Epiblast,  38 
Epicardium,    89 
Epidermis,  211 
Epididymis,    172 
Epiglottis,    142 
Epimysium,    T\ 
Epineurium,    82 
Epiphysis,  69 
Epitendineum,   56 
Epithelium 

basal  border  of,  128 

ciliated,  44 

classification,    41 

columnar,  43 

cuticular  border  of,    112 

germinal,    182 

glandular,   46 

goblet,  44,   122 

modified,  41 

neuro-epithelial,    46 

of   mucous   membrane,    46 

pigmented,    45 

prickle,   44 

pseudostratified,   43 

respiratory,    148 

secretory  canals  of,    140 

squamous,  42 

transitional,    45 
Eponychium,    218 
Epodphoron,   188 


Equatorial   plate,   34 
Erectile   tissue,    180,    195 
Erlicki's   solution,   3 
Erythroblasts,  95,    102 
Erythrocytes,    94 
Esophagus 

coats  of,  115 

glands  of,   116 

muscle  of,    117 

vessels  of,    117 
Eustachian  tube,    268 
Excretion,   31 
Exoplasm,   29 
External   ear,   267 
Eyeball 

angle  of  infiltration,   252 

blood-vessels  of,  261 

canal   of  Petit,    259 
Schlemm,   251 
Stilling,   258 

chambers  of,   259 

choroid,  248 

ciliary  body,  248 
muscle,   250 
processes,  249 
ring,   249 

cornea,    245 

hyaloid  canal,  258 

iris,   250 

lens,   258 

lymph   channels  of,   261 

optic  nerve,   257 

refractive  media,  258 

retina,  252 

sclera,   245 

venal   vorticosae,    261 

vitreous  humor,  258 
Eyelashes,   264 
Eyelid, 

bloodsupply,  265 

caruncle,  265 

cilia,  2.(iA 

conjunctiva,    264 

glands,  264 

lymphatics,  265 

nerves  of,  265 

plica  semilunaris,   265 

tarsus,   2(i2 

third,  265 

F. 

Fallopian  tube,    188 
Farrant's  solution,  21 
Fascia,    57 
Fat,   58 

cells,    59 

crystals,    59 

stains   for,    59 
Female  genital  system,    182 
Fenestra    rotunda,    268 
Fenestrated  membrane  of  Henle,  9.1 
Ferrein,  pyramids  of,    154 
Fertilization,    138 
Fetal   circulation,   208 
Fibre-layer  of  Henle,   255 


INDEX. 


293 


Fibres 

cone,   253 

dentinal,    no 

Mueller's,   254 

muscle 

cardiac,   yd 
intrafusal,  86 
smooth,   75 

voluntary,    72 

nerve,  medullated,   80 
nonmedullated,  80 

neuroglia,   79 
.     rod,   254 

Sharpey's,   64 
Fibro   cartilage,   621 
Fibrous  tissue,   53 
Filar  mass,  28 
Filiform   papillae,    no 
Films,  blood,   23 

Fimbriated  end  of  fallopian  tube,    18 
Fissure  of  spinal  cord,   238 
Fixation,    i 

Fixatives,  see  Fixing  solutions 
Fixing  sections  on  slides,  26 
Fixing  solutions 

alcohol   absolute,    4 

absolute  and  ether,    5 
absolute  and  formalin,   5 
ninety-five  per  cent.,   4 

Bensley's,  3 

chromic    acia,    3 

Erlicki's,    3 

Flemming's,    3 

Formalin,  4 

Golgi's,  3 

Heidenhain,    i 

Kopsch's,   2 

Mueller's,    2 

Nitric  acid,   4 

Orth's,   3 

osmic  acid,  3 

potassium  bichromate,    i 

Tellyesnicky's,    2 

Zenker's,    2 
Flemming's    solution,    3 
Fluids,   see  Fixing  solutions 
Folds   of    Kerkring,    125 
Foliate  papillae,   283 
Follicles 

agminated,    ''q 

Graafian,   182 

hair,   216 

lenticular,    118 

solitary,    59,    128 
Folliculi,   theca,    182 
Fontana,  spaces  of,  251 
Foramen  cecum,    in 
Foramina  nervosa,   278 
Formaldehyde,   4 
Formalin,  4 
Formative  yolk,    184 
Formatio  reticularis,   2z(i 
Fovea  centralis,  257 

Howship's,  66 
Freezing  tissue,  10 
Filliform  papillae,   in 


Gatactophorous  ducts,   223 
Gall-bladder,   136 
Ganglia,  82 

spinal,  243 
Ganglion   cells,    82 

bipolar,  79 

multipolar,    79 

unipolar,    79 
Ganglion    spirale,    278 
Gastric  glands,    118 

pits,    117 
Gastrula,    39,    119 
Gelatin  injection  mass,   22 
Genital  corpuscles,   83,    286 

organs,    female,    182 
male,    169 
Genitalia,    195 
Germinal   center,   60 

epithelium,    182 

spot,  37,    184 

vesicle,    ZT^    184 
Germ-nucleus,    186 
Giant  cells,  37 

Gianuzzi,   crescents  of,    140,    141 
Giraldes,  or^an  of,   181 
Glacial    acetic   acid,    i 
Glands 

accessory    tear,    263 

alveolar,    50 

alveolo-tubular,   50 

arterial,    99 

Bartholin's,    196 

Bowman's,    284 

Brunner's,    126 

bulbo-urethral,    196 

cardiac,    118 

carotid,    99 

ceruminous,    267 

coccygeal,    99 

coiled,    50 

Cowper's,    179 

digestive,  132 

ductless,    5 1 

duodenal,    126 

excretory,    52 

fundus,   118 

intestinal,    122 

Krause's,   263 

labial,    10 1 

lacrimal,   266 

lenticular,    118 

Lieberkuehn,    122 

lingual,    113 

Litre's,  164,   165 

Luschka's,    99 

lymphatic,    100 

mammary,    220 

Meibomian,    264 

mixed,    52,    138 

Moll,    264 

Montgommery's,   224 

mucous,    52,    137 

olfactory,    284 

pancreas,    139 

parathyroids,    1 52 


294 


INDEX. 


Glands  (continued) 
parotid,    139 
peptic,    118 
pineal,   232 
pituitary,   231 
preputial,    180 
prostate,    177 
pyloric,   120 
racemose,    50 
saccular,   50 
salivary,    137 
sebaceous,  220 
serous,    51,    138 
structure  of,    138 
sublingual,    139 
submaxillary,    141 
sudoriparous,    219 
suprarenal,    166 
sweat,    219 
tarsal,    264 
tear,   263 
thymus,    104 
thyroid,    151 
tubular,  49 
tubulo-alveolar,    50 
Tyson's,    180 
urethral,    164 
uterine,    190 
varieties    according    to    secretion, 

51 

structure,  48 
Glandular  cells,   46 
Glans,  clitoris,    196 

penis,    179 
Glassy  membrane,  249 
Glisson's   capsule,    132 
Glomerular    layer    of    olfactory    lobe, 
230 

adrenal,    166 
Glomerulus,    156,    230 
Glomus  caroticum,  99 

coccygeum,    99 
Glycerin    albumen,    25 

jelly,    21 
Glycogen,   29,    136 
Goblet  cells,  44,    122,   126,    128 
Gold  chlorid,    16 

stain,    16 
Golgi   cells,    79 

fixing   solution,    3 

silver  stain,    17 
Goll,    columns  of,    242 
Gower,    columns    of,    242 
Graafian    follicles,    182 
Granular  cells  of  cerebellum,   234 
Granule  cells  of  Graafian  follicle,    182 
Gray   commissure,    242 

matter,   78,  227 
Grenacher's  carmin,   14 
Ground  substance  of  cartilage,  62 

of  bone,   64 
Growth,   32 
Gum,    9 
Gustatory 

hair,   iii,  283 

organ,    in,    283 

pore.    III,  283 


H. 

Hair 

auditory,    272 

bulb,    215 

color   of,    218 

follicle,    215 

lanugo,   218 

layers  of,   217 

muscle,   218 

olfactory,    281 

papilla,    216 

root,    215 

root-sheaths,   217 

shaft,    215 
Hair-cells,    271,    277 
Hardening   agent,    5 
Hassal's   corpuscles,    103 
Haversian    canals,    66 

lamellae,    66 
Heart,  88 

annuli  fibrosi,   88 

blood-vessels   of,    89 

chordae  tendineae,  88 

corpus  Arantii,   89 

elastic   tissue,    88 

endocardium,   88 

epicardium,   89 

lymphatics,    89 

muscle,   76 

myocardium,   89 

nerves  of,   89 

pericardium,    89 

structure  of,   88 

valves,    88 
Heidenhain,   demilunes  of,    140,    141 

solution,    I 
Helicine   arteries,    180 
Hematoidin  crystals,  96 
Hematoxylin,  acid,   13 

Delafield's,    12 

Harris',   12 

Weigert's,    17 
Hemin   crystals,    96 
Hemaglobin   crystals,   96 
Henle's,  fenestrated  membrane  of,  91 

fibre  layer,   255 

layer,   217 

loop,    157 

limbs,    1 57 
Hensen's   cells,    275 

disc,    72 
Hiatus,    128 
Howship's  lacunae,   66 
Humor   aqueous,    258 

vitreous,   258 
Huxley's   layer,   217 
Hyaloid   artery,   258 

canal,  258 

membrane,   258 
Hyalin   cartilage,   62 

cells,  96,    100 
Hyaloplasm,    28 
Hymen,   195 
Hypoblast,   39 
Hypophysis,  231 


INDEX. 


^95 


Ileum,    126 
Imbedding 

celloidin,    8 
gum,  9 
paraffin,    6 
Indirect   division,   33 
Infiltration   angle,    252 
celloidin,    8 
gum,  9 
paraffin,  6 
Injection,   21 
Inner    cell-mass,    39,    198 
Inner   bulb,    84,    285 
Intercellular  bridges   (spines).   44.    211 
substance,    41,    55»    62,    64,    78,    s.- 
Interfilar    mass,    28 
Interglandular    projection,    117 
Interglobular   spaces,    109 
Intermediate    disc,    73 

tubule,    138 
Internal  ear,   269 

elastic   lamina,    90 
Interstitial  cells  of  ovary,   188 

of  testicle,    172 
Intervillous  spaces,   207 
Intestine 

agminated   follicles  of,    126 

blood-vessels  of,    130 

Brunner's   glands,    126 

crypts  of,    22 

epithelium  of,    122 

goblet  cells  of,    122,    126,    128 

folds  of  Kerkring,    125 

large,    126 

lymphatics,    130 

mucosa  of   large,    126 

of   small,    122 
muscular   coat  of  large,    126 

of  small,    126 
muscularis    mucosae,     123 
nerves  of,    130 
Peyer's  patches  of,    126 
plica   circulares,    125 
solitary    follicles,     122 
submucosa   of   large,    128 

of   small,    126 
valvulae    conniventes,    125 
villi,    123 
Intima   of   artery,    90 

of   vein,    93 
Intra-cartilagenous    bone,    68 
Intrafusal   muscle   fibres,    86 
Intra-membranous  bone,   71 
Intumescentia   cervicalis,    237 

lumbalis,    237 
lodin,   26 
Iris 

anterior    endothelium,    250 

lamina,   250 
muscle,   250 
pigment,    251 
posterior    epithelium,    251 

lamina,    251 
stroma,   250 
Irritability,   32 
Islands   of   Langerhans,    134 
Isotropic,   72 


J. 

Jejunum,    126 
Jelly,    glycerin,    21 
Wharton's,    208 

K. 

Karyokinesis,  33 
Katabolism,   31 
Keratohyalin,    212 
Kerkring,    folds    of,    125 
Kidney 

arched  tubules,    158 
arches,    arterial,    159 

venous,    160 
blood-vessels  of,    158 
Bowman's  capsule,    156 
capsule  of,   154 
columns  of  Bertini,  157 

of    Ferrein,     155 
convoluted  tubules,   157 
cortex,    154 
ducts  of   Bellini,    156 
Henle's  limbs,    157 

loops,    157 
hilus,    154 
interlobular    arteries,     160 

veins,    160 
labyrinth,    155 
lymphatics,    161 
Malpighian   bodies,    156 
pyramids,    156 
medulla,    156 
medullary  pyramids,    156 

rays,    1 54 
nerves  of,   161 
papillary  ducts,    156 
pelvis,    157  .   ,  . 

pyramids    Malpighian,    156 

of  Ferrein,  154 
renal  corpuscle,  156 
sinus  of,   154 

straight  collecting  tubules,    157 
tubules,    157 

diameter   of,    158 
uriniferous,    157 
venae  stellatae,    160 
Kopsch's  fluid,   2 
Krause,   corpuscles  of,   285 
gland  of,   263 
membrane    of,    73 


Labia   majora,    196 

minora,    197 
Labyrinth,    bony.    269 

membranous,    269 

of   kidney,    155 
Lacrimal  apparatus,   265 

canaliculi,    266 

caruncle,    265 

gland,    266 

accessory,     263 

sac,  266 
Lacteal,  124 
Lacunae,   bone,    66 

corneal,   246 

Howship's,    66 

trophodermal,  201 


296 


INDEX. 


Lamellae    of    bone 

circumferential,    65 
concentric,  66 
external,    65 
ground,   66 
Haversian,    66 
intermediate,   66 
internal,   66 
perimedullary,    66 
periosteal,  65 
peripheral,   65 
Lamellar  corpuscles,  83 
Lamina   basilaris,    272 
cribriform,    256 
cribrosa,    245 
elastic,    anterior,    250 
external,  90 
internal,   90 
posterior,    250 
fusca,   245 
spiralis,  274 
suprachoroidea,    248 
Langerhans,  areas  of,    139 
Langhans,  layer  of,  203 
Lantermann,   clefts  of,  80 
Lanugo   hairs,  218 
Large  intestine,    126 
Larynx 

blood-vessels  of,    143 
cartilages  of,    143 
coats  of,    143 
epiglottis,    142 
nerves  of,   144 
ventricles,    143 
vocal  cords,    143 
Lateral  discs,  73 
Lens,    crystalline,    258 
capsule  of,  258 
epithelium  of,  259 
fibres  of,   259 
ligaments  of,   259 
Lenticular  glands   (follicles),    118 
Leukocytes 

classification  of,  96 
Leydig's  cells,    172 
Lieberkuehn's  glands,    122 
Ligamentum  nuchae,   57 
pectinatum,   252 
suspensorium,    259 
Ligamentum   spirale,   274 
Limbus,  274 

Limiting  membrane  of  retina 
^  external,    254 

internal,    254 
of  vessels 

arteries,    90 
veins,    03 
Lingual 

glands,    113 
papillae,    110 
septum,    113 
tonsil,   113 
Linin,   30 
Lip,    106 
Liquor   folliculi,    183 

sanguinis,    97 
Lissauer,  column  of,   242 
Lithium  carbonate,   18 


Litr6,  glands  of,    164,    165 
Liver 

bile-capillaries,    134 
blood-vessels  of,    134 
capsule,    132 
cells,    133 
circulation  of,    135 
function  of,    136 
hepatic  duct,    137 
interlobular  ducts,    134 
tissue,   134 
vessels,    134 
lobule,   133 
lymphatics,    136 
nerves  of,    136 
pig's,   132 
portal  system,    134 

vein,    134 
reticulum  of,    132 
Loop,   Henle's,    157 
Lungs 

air-sacs,    149 

alveolar    ducts,    148 

alvei,    147 

alveoli,    149 

blood-vessels  of,    149 

circulation   of,    149 

lobules,   147 

lymphatics,    150 

nerves  of,    150 

pleura,    146 

respiratory  bronchiole,    148 

epithelium,    148 
terminal    bronchiole,    148 
vestibulum,   149 
Lunula,    219 
Luschka's  gland,   99 
Lutein 

cells,   187 
Lymphatic  system,  100 
Lymph  capillaries,    100 
ducts,    100 
vessels,    100  . 

Lymph  follicles 

agminated,   60,    126 
germinal   center  of,    60,    126 
of   appendix,    128 
of  intestine,    1 18,    122 
of  pharynx,    115 
of  tongue,    113 
of  tonsil,    114 
solitary,   60,    114 
Lymph   glands    (nodes) 
blood-vessels  of,    102 
cortex,   100 
hilus,    10 1 
lymph   sinuses,    loi 
medulla,    10 1 
medullary   cords,    10 1 
nerves,   102 
structure  of,  100 
Lymph  node,   see  Lymph  gland 
Lymphocytes,   59,  96,   100 
Lymphoid    tissue 
dense,   60,    100 
diffuse,    100 


INDEX. 


297 


M. 

Macroblast,  95 
Macrocyte,  94 
Macula   acustica,    270 

lutea,    257 
Male  genital   organs,    169 
Malpighian   body,    156 

corpuscle,    103 

pyramid,    156 
Mammary  gland 

ampulla,   22^ 

areola,  224 

cells  of,  222 

colostrum,    22^ 

galactophorous    ducts,    22:^ 

glands  of  Montgommery,   224 

lactating   and   nonlactating,    22^ 

nerves  of,   224 

nipple,    22^ 

structure  of,  222 
Mammilla,  22;^ 
Margarin  crystals,    59 
Marrow 

cells  of,   67 

cavity,  67 

red,    67 

serous,    67 

spaces,   68 

yellow,  67 
Marrow  cells,  67,  97 
Mast-cells,   97 
Matrix  of  nail,  219 

cartilage,    62 
Maturation  of  ovum,  Z7,    186 
Mayer's  albumen,    25 

solution,    1 1 
Median  disc  of  Hensen,   72 
Media,  of  artery,  90 

of  vein,  93 
Mediastinum  testis,   169 
Medullary  cavity,  67 

cords,   10 1 

pyramids,    156 

rays,   154 

sheaths,  80 
Medulla 

of  adrenal,   166 

of  bone,   67 

of  cerebellum,   234 

of  cerebrum,  2^7 

of  hair,  217 

of  kidney,    156 

of  lymph  node,    10 1 

of  ovary,    188 
Meibomian  glands,   264 
Meissner's  corpuscles,  83,  284 

plexus,    130 
Membrana   basilaris,    272 

granulosum,    182 

nictitans,   265 

olfactoria  limitans,  ^81         / 

reticularis,   277    ,-^         1.    ..,r    «; 

tectoria,  275  V"',;^ 

Membrane  .       -».      ,«<^ 

basement,   46 

basilar,  272 

Bowman's,  246 

Corti's,   278 


Membrane    (continued) 

Descemet's,   246 

elastic,  90 

fenestrated,  of  Henle,  91 

glassy,   249 

hyaloid,   258 

Krause,   72i 

mucous,  46 

otolith,  271 

periodontal,    no 

of  cell,   31 

of  retina  external   limiting,   254 
internal   limiting,    254 

Reissner,  272 

serous,  46 

tympanic,   267 

vitelline,   Z7y    184 
Menisci,  83 

Menstruation,  changes  of,   192 
Mesoblast,   39 
Mesoderm,   39,    192 

derivatives,   40 
Mesothelium,   46 
Metabolism,   31 
Metakinesis,  35 
Metaphase,  35 
Methylene  blue,    13 
Methyl  green,    13 
Microblast,  95 
Microcyte,   94 
Microsome,  28 
Middle  ear,  268 
Milk,   22Z 
Mitosis,  ZZ 
Mitral   cells,    231 
Monaster,   3 1 
Mother  star,   34 
Mixed  connective   tissue,   58 

glands,    52,    138 
Modiolus,   272 
Molecular  layer 

of  cerebellum,  232 

of   cerebrum,    229 

of  olfactory   bulb,    231 

of  retina,  255,  256 
Moll,  glands  of,  264 
Mons  veneris,    196 
Montgommery's  glands,   224 
Morula,  39 
Mossy  cells,  79 
Mother  cell,   174 

nucleus,   34 

skein,   34 
Motion,  32 
Motor  cells,  238 

endings,   85 

roots,  243 
Mounting,   20  , 

Mouth,   107 
Mucin,  44,  122 
Mucous  connective  tissue,   57 

glands,   50,    137 
Mulberry  mass,  39  . 

Mueller's  fibres,  254     '  '   \,       ,;, 

lid  muscle^   264    '      ^' 

ring  muscle,  249 

solution,  2 


298 


INDEX. 


Muscle 

of  blood-vessels,   75 

structure  of  a,  73 

vein,  75 
Muscle  fibre 

branched,  76 

cardiac,   76 

Cohnheim's  fields,    73 

fibrillae  of,  72 

involuntary,  75 

nuclei,   73,   77 

sarcolemma,    73 

sarcoplasm,    72 

sarcous  elements,   72 

smooth,   75 

striations,   73,   76,   77 

voluntary,  72 
Muscle-spindle,  86 
Muscularis  mucosae,  46 
Myelin   sheath,   80 

stain,    17 
Myeloc>te,  67,  97 
Myeloplaxes,  67 
Myocardium,  89 

N. 

Nabothi,   ovuli,    191 
Nails 

bed,  219 
body,    218 
eponychium,    218 
fold,    218 
groove,    218 
lunula,  219 
matrix,  219 
root,  2i8 
wall,  218 
Nares,   142 
Nasal  mucosa 

blood-vessels  of,   282 

Bowman's  glands,    281 
lymphatics,   282 
nerves  of,   282 
olfactory  area,  280 
respiratory   portion,    280 
Nerve  cells 

axis-cylinder,    78 

bipolar,  79 

Deiter's,   79 

dendrites,    78 

first  type,   79 

Golgi's,   79 

multipolar,   79 

neurit,   78 

neuron,   78 

second  type,  79 

structure,    78 

telodendrites,    79 

unipolar,  79 
Nerve-endings 

classification,   82 

conjunctival,  83 

corpuscles  of  Meissner,  83,   284 
of  Vater,  84,  285 
of  Wagner,   83,   284 

end-bulbs,  83 

genital,  83 


Nerve-endings  (continued) 

in   epithelium,   82 

smooth  muscle,   85 
voluntary    muscle,    85 

motor,   85 

neuromuscular,    86 

neuro-tendinous,    87 

Pacinian   body,   84,   285 

Ruffini,  86 

sensory,   82 

tactile  cells,  83 

corpuscles,   83 
Nerve  fibre 

axis-cylinder,  80 

internode,    80 

medullary    sheath,    80 

medullated,   80 

myelin,     80 

neurilemma,    80 

nodes  of   Ranvier,   80 

nonmedullated,   80 

sheath  of  Schwann,   80 

white   substance  of   Schwann,   80 
Nerve  trunk 

blood-vessels  of,   82 

endoneurium,  82 

epineurium,    82 

lymphatics,   82 

myelin,  80 

perineurium,    82 

sympathetic,  80 
Nervi  nervorum,  82 

vasorum,  94 
Nervous  system,  226 

tissues,   78 
Neurilemma,   80 
Neuro-epithelium 

of  ear,   271,  277 

of  eye,   254 

of  nose,  281 


of  retina,   254 
'  uds, 


283 


of  taste  bud 
Neurofibrils,    78 
Neuroglia,    79 

cells  of,  79 

fibres,  79 
Neuron,  78 
Neutrophil,  97 
Nissl's   bodies,    78 
Nitric  acid,   4 
Nodes  of   Ranvier,    80 
Nodules 

cortical,    100 

lymph,   60,    100 

secondary,    100 

solitary,   60,    100,    122,    127 
Normoblasts,   95 
Nuclear 

division,   34 

matrix,    29  , 

membrane,   29       ; 

sap,  29 

spindle,   36 
Nucleolus,   30 
Nucleus 

achromatin,    30 

chromatin,   30 

cuneatus,   236 


INDEX. 


299 


Nucleus  (continued) 

daughter,   36 

gracillis,    236 

resting,   29 

Stilling,    240 
Nuel,   spaces  of,   27 ^ 
Nutritive  yolk,    184 
Nymphae,    196 

O. 
Odontoblasts,    109 
Oils   for  clearing 

anilin,    20 

anilin-xylol,   20 

bergamot,  20 

benzol  of,   20 

cedar-wood,  20,  6 

clove,   19 

creosote,    19 

origanum,    19 

turpentine,  6 

toluol,   7,    20 

xylol,   6,   20 
Olfactory  lobe 

glomerular  layer,  230 

granular  layer,   231 

mitral  cells,   231 

molecular  layer,   231 

peripheral  fibres,  230 
Olfactory   mucosa 

blood-vessels    of,    282 

cells  of,   280 

glands  of,   281 
Olivary  bodies,  230 
oocyte,    185 
Optic  nerve,  257 

papilla,  257 
Orange,   14 
Ora  serrata,   257 
Oral  cavity,    107 
Organ  of  Corti,   275 
Orth's   solution,    3 
Osmic  acid  fixative,   3 

stain   for   fat,    59 
Osteoblasts,   65 
Osteoclasts,    65 
Ossicles,   auditory,   268 
Ossification 

endochondral,    68 

intra-membranous,  71 
Otolith   membrane,    271 
Otoliths,  271 
Outer  cell-mass,   198 
Ovary 

antrum  of  follicle,    183 

blood-vessels  of,    188 

corpus  albicans,    187 

hemorrhagicum,  .186 
luteum,    187 

cortex,    182 

egg  tubes  of  Pflueger,   184 

germinal  epithelum,    182 

Graafian  follicle,    182 

hilus,    182 

interstitial  cells,   188 

lymphatics,    188 

medulla,    188 

muscle  tissue  of,    188 

nerves  of,    188 

tunica  albuginea,    182 


Oviduct,   188 
Ovulation,    187 
Ovuli   Nabothi,    191 
Ovum 

dentoplasm,    38,    184 

escape  of,    187 

fertilization,    38 

formative  yolk,  38,   184 

maturation,    ■^'j,    186 

nutritive   yolk,    38,    184 

segmentation,    39 

structure,  37 
Oxyntic  cell,  118 
Oxyphil,    see   Eosinophil 

r. 

Pacchonian  bodies,  226 

villi,    226 
Pacinian  bodies,  84,  285 
Palatine  tonsils,    113 
Pancreas 

areas  of  Langerhans,   139 

blood-vessels  of,    139 

cells  of,   139 

centro-acinar    cells,    139 

ducts,    139 

nerves  of,   139 

zymogen  granules,    139 
Pancreatic  duct,    139 
Panniculus  adiposus,   213 
Papilla 

circumvallate,    in 

filliform,    no 

foliate,   283 

fungiform,    in 

hair,  216 

of  mucosa  of  tongue,   in 
esophagus,    115 

optic,   257 

tactile,    196,   212 

vascular,    196,   212 
Paracarmin,    15 
Paradidymis,   181 
Paraffin 

fixation    of,    sections,    25,    26 

infiltration,    6 

removal   from  sections,   20 

sectioning,  10 
Parathyroids,  152 
Paroophoron,  188 
Parotid  gland,  139 
Parovarium,  188 
Pars  ciliaris  retinae,  249 

iridica  retinae,  251 

optica  retinae,  252 
Pectinate   ligament,    252 
Pelvis  of   kidney,    157 
Penis 

arteries  of,    180 

corpora  cavernosa,    180 

corpus  spongiosum,   180 

emissary  veins,    180 

erectile  tissue,    180 

glands  of  Tyson,    180 

glans,    179,    180 

helicine  arteries,    180 

nerves,    181 

tunica  albuginea,   179 

veins,   180 


300 


INDEX. 


Peptic  cells,   14,   ii8 

glands,    118 
Perforating  fibres  of  cornea,  246 

of   Sharpey,    65 
Pericardium,   89 
Perichondrium,   61 
Periodontal   membrane,    no 
Perimysium,  tz 
Perineurium,  82 
Periosteal  lamellae,   65 
Periosteum,   65 
Peripheral  nerve  endings,  82 
Peritendineum,   57 
Peri  vitelline  space,   184 
Petit's  canal,  259 
Peyer's  patches,    60,    126 
Pflueger's  ^%,z  tubes,   184 
Phagocytes,   96 
Phlangeal  plates,   zyj 

process,  zTy 
Pharynx,    114 

Phloroglucin — nitric    acid,     1 1 
Pia  mater.  226 
Picric  acid  stain,   114 
Picro-carmin,    1 5 
Picro-fuchsin,   14 
Pigment  cells,   45 

of  hair,  218 

of  iris,  250 

of  retina,  253 

of  skin,   213 
Pig's  liver,    132 
Pillar  cells,  zTd 
Pineal  body,   232 
Pinna,   267 
Pits,  gastric,    117 
Pituitary  body,   231 
Placenta 

canalized  fibrin,  206 

cell-knots,   207 

chorion,  205 

decidua,  201 

development  of,    198 

intervillous  spaces,  207 

septa  of,  205 

syncytium,   207 

villi  of,  207 
Plasma  cells,  55 
Plastids,  28 
Platelets  of  blood,  97 
Pleura,   146 
Plexus  of  Auerbach,   130 

of  Meissner,    130 
Plica 

circulares,    125 

palmatae,   191 

semilunaris,   265 
Polar  bodies,    186 

field,   34 
Polynuclear   cells,   96 
Pons,   234 
Portal   circulation,    134 

system,    134 

vein,    134 
Potassium  bichromate,   i 
Precapillary  vessels,   92 
Prepuce,    180 
Prickle  cells,  44,  211 


I    Primary  marrow  cells,  68 

spaces,  68 
Prochorion,    200 
Prominentia  spiralis,  ztz 
Prophase,  34 
Prostate 

blood-vessels,    179 

capsule,    177 

glands,   178 

nerves,    179 
Prostatic  bodies,   178 
Protoplasm,  28 
Prussian  blue,  22 
Pseudostratified   cells,   43 
Pulp  cavity,    109 

splenic,    102 

tooth,   109 
Pupil,  251 
Purkinje   cells,   22,2 
Pyramidal 

cells  of  cerebrum,   228 

columns,   direct,   242 
crossed,  242 
Pyramids 

Malpighian,    1 56 

medullary,   156 

of  Ferrein,   154 
Pyrenin,    31 

R. 
Ranvier,  nodes  of,  80 
Receptaculum  chyli,    130 
Rectum,   127 

valves  of,   127 
Red  blood  cells,  94 

bone  marrow,   (i7 
Reissner's  membrane,  2^2 
Remak's  fibres,  80 
Renal  corpuscles,    156 

pelvis,    157 
Reproduction,   32 
Respiratory 

bronchiole,    148 

organs,    142 

region,    142 
Restiform   bodies,    22,7 
Rete  Malpighii,  211 

testis,    172 
Retia  mirabilia,  92 
Reticular   connective   tissue,    58 

gland,  50 
Reticulum,  58 
Retina 

amakrine   cells,   256 

blind  spot,  257 

blood-vessels,  259 

central  artery,  259 

cone-cells,  253 

cone-fibres,   253 

fovea   centralis,    257 

ganglion  cells,  256 

Henle's  fibre  layer,   255 

limiting  membrane,   inner,   254 
outer,  254 

macula  lutea,  257 

molecular   layer,    inner,    256 
outer,  255 

nerve  fibre  layer,  256 

optic,  257 


INDEX 


3o> 


Retina   (continued) 

optic  nerve  papilla,  257 

ora  serrata,  257 

pars  ciliaris,    249 
iridica,   251 
optica,  252 

pigment  layer,  253 

rhodopsin,   254 

rod-cells,  254 
fibres,  254 

visual   purple,   254 
Rod-cells,   254 

fibres,   254 
Rolandi,   substantia  gelatinosa,    240 
Root  sheaths,  217 
Rouleaux,  94 
Ruffini,  end-organs  of,  87 


S. 

Sacculations  of  colon,    127 

Sacculus,   270 

Safranin,    13 

Salivary    corpuscles,    1 14 

glands,    137 
Sarcolemma,   yz 
Sarcoplasm,  yz 
Scala  media,  z-j^ 

tympani,   272 

vestibuli,  zyz 
Schlemm's  canal,   251 
Schwann, .sheath  of,  80 

white   substance  of,   80 
Sclera,  245  _ 

Scleral  conjunctiva,  245 
Sebaceous  glands,    220 
Sebum,  221 

Secondary   marrow   spaces,    68 
Secretion,   31,    151 
Secretory  canals,    140 
Sectioning   celloidin,    10 

paraffin,    10 
Sections,  staining  of,  26 
Semen,   175 

Semi-circular  canals,   271 
Seminiferous  tubules,    170,   171 
Seminal  vesicles,   177 
Sense  of  smell,   283 

taste,  283 

touch,  284 
Sensory  endings,  82 
Septa,    placental,    205 
Septum  linguali,  113 

posterior  median,   238 
Serous  glands,   51,    138 

membranes,   46 
Sertoli's  columns,    171 
Sharpey's   fibres,    64 
Sheath  Henle's,  217 

Huxley's,    217 

medullary,   80 

myelin,   80 
Silver   staining 

blood-vessels,    17 

lymphatics,    17 

nervous  tissue,   17 


Sinus  lactiferous,  223 

marginal,  207 

lymph,    10 1 

of  kidney,   154 
Sinusoids,  92 
Skein,    daughter,    36 

dense,   34 

loose,  34 

mother,    34 
Skin 

appendages,  215 

arrector  pili  muscle,  218 

blood-vessels  of,  214 

color  of,   214 

corium,  212 

derma,  212 

epidermis,  211 

glands,   219 

layers  of,   211 

lymphatics,    215 

panniculus  adiposus,   214 

pigment,   214 
Slides,  2(i 

Small   intestine,    122 
Smell,    283 
Smooth  muscle,    75 
Sole-plate,  85 

Solitary   follicles,   60,    122,    128 
Somatopleure,    199 
Spaces  of  Fontana,   251 

of  Nuel,  2Ty 
Spermatid,    174 
Spermatoblast,    175 
Spermatocyte,   174 
Spermatogenesis,    174 
Spermatogonia,    171,    174 
SpermatozoSn,    38,    173 
Spider  cell,    79 
Spinal  cord 

blood-vessels  of,  241 

canal,  240 

cells,   248 

commissures,   240 

columns,    241 

fissure,    238 

gray  substance,  238 

horns,   38 

membranes  of,  226 

septum,  238 

white  matter,  241 
Spindle,    central,    35 

nuclear,    36 
Spinal  ganglion,  24^5 
Spirem,  34 

Splanchnopleure,    199 
Spleen 

capsule,   102 

circulation,   103 

corpuscles,     103 

lobules,    104 

Malpighian  corpuscles,  103 

pulp,    102 

trabeculae,   102 
Spongioplasm,   28 
Spongy  bone,  64 
Spot,   germinal,   37,    184 
Staining  of  sections,  26 


302 


INDEX. 


Stains 

acid,  14 

acid    hematoxylin,    13 

alum  carmin,    15 

anilin  dyes,   13 

basic,    12 

bismark  brown,    13 

borax    carmin,    14 

carmin,    14 

Delafield's  hematoxylin,    12 

Ehrlich-Biondi-Heidenhain,    16 

elastica,    19 

eosin,    14 

eosin-methylene  blue,  24 

for  adipose  tissue,  59 

fold,    16 
[arris*   hematoxylin,    12 

hematoxylin  acid,    14 
Delafield's,    12 
Harris',    12 

methylene  blue-cosin,  24 

methyl  green,    13 

myelin,    17 

nuclear,   12 

orange,   14 

osmic   acid   for   fat,    59 

paracarmin,    15 

picric   acid,    14 

picro-carmin,   15 

protoplasmic,    14 

silver,    17 

safranin,    13 

Sudan    III   for   fat,    59 

Van  Gieson,   14 

Weigert's  elastica,    19 
myelin,    17 

Wright's  blood,  24 
Stars,   daughter,   36 

mother,   34 
Stellate  cells,    53 
Steno's  duct,   139 
Stomach 

acid  cells,    119 

blood-vessels,    121 

cardiac  end,    118 

coats,    117 

glands,   118 

lymphatics,    121 

mucous  membrane,   117 

nerves,    122 

peptic   cells,    118 

pyloric  end,    112 
Stratum   corneum,    211 

germinativum,   211 

granulosum,  212 
of  ovary,    183 

lucidum,   212 

Malpighii,   211 

mucosum,    192 

papillare,    212 

reticulare,    213 

supra  vasculare,    192 

vasculare,    192 
Stria  vascularis,  273 
Stilling 

canal  of,   258 

nucleus  of,  240 
Subarachnoid  space,   226 


Subdural    space,    226 
Subscleral,   245 
Sublingual  gland,   139 
Submaxillary   gland,    14 
Substantia  gelatinosa,   240 

grisea   contralis,    240 

propria,    246 

spongiosa,  241 
Succus   entericus,    126 
Sudan   III,    59 
Sudoriparous  glands,   219 
Sulcus   spiralis,    275 
Suprarenal  body 

blood-vessels,    167 

cells,    166 

cortex,    166 

medulla,    166 

nerves,    168 

zones,    166 
Suspensory  ligaments  of  lens,  259 
Sustentacular  cells,   iii,  254,  270,  277, 

280,   283 
Sweat-glands 

blood-vessels,    220 

cells  of,  220 

lymphatics,    220 

modified,  220 

nerves,  220 

pore,  220 
Sweat-pore,  220 
Syncytum,  203 

T. 

Tactile  cells,  83 

corpuscles,  83,  284 

menisci,   83 

papillae,    196,    212 
Taenia  coli,    127 
Tapetum   cellulosum,   248 

fibrosum,    248 
Tarsal  glands,   264 

plates,   262 
Taste-buds,   iii,   142,  283 

pore,   III,   283 
Tear  gland,   266 

accessory,   263 
Technic  general,    1 

slide,   25 
Teeth  auditory,    27  f^ 

cementum,    108 

crown,    107 

dentin,   107 

enamel   107. 

fang   107. 

nerves    109. 

pulp    109. 

root  107. 

root  canal  109 

vessels  of    109 
Teichmann's  crystals,   92 
Tellyesnicky's  solution,   2 
Telophase,  36 
Tendon    56 

cells    57 
Tenon  capsule  of  266. 

space  of  266. 
Terminal  bronchioles   148. 


INDEX. 


303 


Testicle 

blood-vessels,    173 

excretory   tubules,    171,    172 

interstitial   cells   172. 

lobules   of    170. 

lymphatics    173 

mediastinum,    169 

nerves    173. 

seminiferous  tubules,    170 

tunica  albuginea,   169 
vaginalis    169. 
Theca   folliculi,    182 
Third   eyelid,   265 
Thymus 

blood-vessels,    105 

changes  in    104 

corpuscles  of  Hassal   105 

cortex    105 

medulla    105. 
Thyroid    body 

blood-vessels,    152 

colloid  substance   151. 

lymphatics    152. 
Tigroid   bodies   78. 
Tissue 

areolar,    58 

adipose  58. 

connective    53. 

definition  of  41. 

elastic  56. 

embryonic   57. 

epithelial,   41 

erectile  180,   195, 

fibrous   55. 

lymphoid    59. 

mucous,  57 

muscular 

cardiac  76. 
smooth  75. 
voluntary  ^2. 

nervous    78 

retiform    58. 
Toluol  7,  20. 

Tome's  granular  layer,   109 
Tongue 

blood-vessels,    113 

glands,    113 

lymphoid  tissue   113. 

muscle   III. 

papillae,   no 

taste-buds    1 1 1. 
Tonsil 

crypts  of,    113 

lingual    113. 

palatine    113. 
Touch   284. 
Trachea    144. 
Transitional  cells,  45 
Trichloracetic  acid,    11 
Trigonum  vesicae,   166 
Triploblast,  39 
Trophoderm,    199 
Trophodermal   lacunae,   201 
Tubular    glands 

coiled   50 

compound  50 

branched    50 


Tubular  glands  (continued) 
reticular   50 
simple  49 
Tubules 

dentinal    109 
intercalated,    138 
intermediate,    138 
secretory    138. 
seminiferous    170. 
uriniferous,   157 
Tubuli    recti    171. 
Tubulo-alveolar  glands,   50 
Tunica  adventitia,  90 
Tunica  albuginea  ovary,    182 
pelvis,    180 
testicle  169. 
externa   artery   90 
eye  245. 
vein  94 
interna  artery  90 
eye  245 
vein  94. 
media   artery   90 
eye  245. 
vein  94 
propria  46 
vaginalis   169 
Tunica   vasculosa,    182 
Tunnel  of  Corti,  276 
Turpentine  6. 
Tympanic   cavity   268. 
lamella  275 
membrane  267 
Tympanum    268. 
Tyson's   glands    180. 

U. 

Umbilical   cord  208. 
Units  functionating,   138 

secreting    138. 

structural   138. 
Ureter   162 
Urethra 

female  164 

male  164 
Urinary  bladder,   163 

organs   154. 
Uriniferous  tubule,   157 
Uterus 

blood-vessels  of,   193 

cervix    190. 

glands  190. 

lymphatics  193. 

menstrual   changes   192 

mucosa    190. 

nerves    193. 

ovuli  Nabothi   191. 
Utriculus,  270 
Uveal   tract,   247 


Vacuoles  29. 

Vagina  194 

Valves  of  heart  88. 

veins  93. 
Valvulae  conniventes,    125 
Van  Gilson's  stain,  14  . 


304 


INDEX. 


Vasa  efiferentia,   172 
Vasa  vasorum  94. 
Vascular  papillae   196,  212. 
Vas  deferens,   176 
Vater-Pacinian  body,   84,   285 
Veins 

central    132 

coats  of  93. 

portal,   134 

valves  of  93. 
Venae  archiformes,   160 

rectae,    160 

stellatae,    160 

vorticosae,   201 
Ventricles  of  larynx   143. 
Vermiform   appendix,    127 
Vesicle 

blastodermic  39 

entodermal    199 

germinal  37,    184. 

seminal    177. 
Vestibule 

of  vagina   195. 
Villi  chorionic,   203 

of  oviduct,   189 

of  placenta  207. 

of  small  intestine   123. 
Visual  cells,  254 
Visual  purple,  254 
Vital  phenomena  31. 
Vitelline  membrane,  37,  184 
Vitellus    37,    184 
Vitreous  humor,  258 
Vocal  cords   143 
Volkmann's  canals,  66 
Voluntary  muscle   T2. 

W. 

Wagner,   corpuscles  of,  83,   284 
Wandering   cells   53. 
Wei'^ert's  elastica  stain,   17 


Weigert's  myelin  stain,    19 
Wharton's  duct   141. 

jelly  208. 
White  blood  cells  96 

commissure,   240 

fibrous  tissue  55 

matter   80,    22T. 

substance  of  Schwann,  80 
Wirsung's  duct    139 
Wright's  blood  stain  24. 

X. 

Xylol   6,  20. 
Xylol,  anilin  oil,  20 
Xylol  balsam,  20 
Xylol,  carbol,  20 

Y. 

Yellow  bone  marrow  67. 

elastic   tissue    57. 

fibro-cartilage   62. 

spot  257. 
Yolk   formative    184. 

nutritive  184. 

Z. 

Zenker's  fluid  2 
Zinn,   zone  of   259. 
Zona 

fasciculata,   166 

glomerulosa   166 

granulosa   183 

pellucida   183 

pectinata,  275 

reticularis,   166 
Zone,   boundary  of  choroid,    248 
kidney,   159 
of  Zinn,  259 


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College  Hospital  ;  Associate  in  Ophthalmology,  Philadelphia  Polyclinic; 
Ophthalmic  Surgeon,  Phoenixville  Hospital,  etc.      With  253  Illustrations. 

Cloth,  net,  ^4.00 

KNIGHT.  DISEASES  OF  THE  THROAT.  A  Manual  for 
Students.  By  Charles  H.  Knight',,  m.d.,  Professor  of  Laryngology, 
Cornell  University  Medical  College  ;  Surgeon  to  Throat  Department, 
Manhattan  Eye  and  Ear  Hospital,  etc.      143  Illustrations.      Cloth,  I3. 00 

WILLIAMS.  MANUAL  OF  BACTERIOLOGY.  By  Herbert  U. 
Williams,  m.d.,  Professor  of  Pathology  and  Bacteriology,  Medical  De- 
partment, University  of  Buffalo.  Third  Edition,  Revised  and  Enlarged. 
With  about  loo  Illustrations.    •  i2mo.  Cloth,  net,  $\.%/^ 

TYSON.    GUIDE  TO  THE  EXAMINATION  OF  URINE.  \^ 
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and  Numerous  Illustrations  Engraved  on  Wood.     Tenth  Editio' 
vised.     l2mo.  Cloth^ 

TYSON.      HANDBOOK    OF    PHYSICAL   DIAGNOP 
Edition,  Revised  and  Enlarged.     With  Colored  an'-' 
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REESE.     MEDICAL  JURISPRUDENCE  ANF 
Sixth  Edition.     By  John  J.  Reese,  m.d.,  Pro^ 
prudence  and  Toxicology,  University  of  Penn'' 

SWANZY.    DISEASES  OF  THE  EYE.    ' 
and  Improved.     Diseases  of  the  Eye  a^ 
book  for  Physicians  and  Students.     Bv 
F.R.C.S.I.,  Surgeon  to  the  National 
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and  Enlarged.      168  Illustratioiv 

BYFORD.      GYNECOLOGY 
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